BIOLOGY  FOR  BEGINNERS 

TRUMAN  J.  MOON 


GIFT   OF 


From  the  collection  of  the 

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San  Francisco,  California 
2006 


CHARLES  DARWIN  1809-1882 


BIOLOGY     FOR 
BEGINNERS 


BY 
TRUMAN  J.   MOON 

MIDDLETOWN,  N.   Y.   HIGH   SCHOOL 


NEW  YORK 
HENRY   HOLT   AND    COMPANY 


- 


COPYRIGHT,  I  Q2  I 

BY 
HENRY  HOLT  AND  COMPANY 


PREFACE 

THIS  text  is  an  attempt  to  present  the  fundamental  facts  of 
elementary  biology  as  clearly  and  briefly  as  a  reasonable  scientific 
accuracy  will  allow.  Three  years'  use  in  manuscript  form  has 
dictated  the  topics  included  and  the  arrangement  followed  in  order 
that  the  book  may  be  easily  taught  and  readily  understood. 

The  course  emphasizes  the  fact  that  biology  is  a  unit  science, 
based  on  the  fundamental  idea  of  evolution  rather  than  a  forced 
combination  of  portions  0f  botany,  •  zoology  and  hygiene. 

Emphasis  has  been  placed  upon  a  logical  arrangement  within 
the  chapters,  so  that  it  is  easy  for  the  pupil  to  study,  outline, 
and  remember  each  lesson. 

A  larger  proportion  of  pages  is  devoted  to  outlines,  tabulations, 
and  diagrams  than  in  any  other  similar  text.  This  means  that 
the  pupil  has  less  text  matter  to  cover,  and  more  help  to  assist 
him  in  doing  it. 

No  laboratory  work  is  included.  Any  laboratory  manual  can 
be  used  with  the  text,  however,  as  it  covers  much  more  than  the 
required  ground.  It  is  thought  that  a  separate  manual  will  allow 
the  teacher  to  emphasize  in  the  laboratory,  those  subjects  which 
he  considers  most  important. 

Experience  has  indicated  that  the  "vocabularies"  save  the 
pupil  much  time  and  confusion.  Particular  care  has  been  taken 
to  keep  the  vocabulary  of  the  text  as  simple  as  possible.  Careful 
explanations  are  made  where  this  seems  advisable.  The  definitions 
in  the  text  are  not  complete,  but,  for  the  sake  of  clearness,  are 
purposely  limited  to  those  meanings  which  fit  the  use  in  the  chapter 
concerned. 

In  any  science  subject  collateral  reading  is  highly  important. 
To  facilitate  this,  lists  of  references  have  been  placed  at  the  ends 
of  the  chapters,  covering  such  books  as  should  be  available  in  a 
well-equipped  school.  This  outside  reading  should  be  encouraged. 

v 

462251 


vi  ACKNOWLEDGMENT 

The  large  number  of  line  drawings  is  intended  to  simplify 
matters  of  structure  for  the  beginner  who  would  have  difficulty 
in  selecting  the  essential  points  of  a  more  detailed  drawing  or 
photograph.  Since  the  object  of  illustrations  in  an  elementary 
text  is  to  call  attention  to  essential  facts,  the  simple  diagrammatic 
outlines  and  complete  labeling  found  in  this  book  are  worthy  of 
notice.  It  is  hoped  also  that  a  reasonable  use  of  line  drawings 
will  help  the  pupil  in  his  own  work  by  affording  models  which 
he  can  easily  approximate. 

The  economic  applications  of  biology  have  been  given  very  full 
treatment,  especially  as  to  their  bearing  on  agriculture  and  civic 
problems. 

The  scope  of  the  matter  presented  is  broad  enough  so  that  the 
teacher  can  select  what  seems  most  important,  and  still  be  sure 
of  covering  any  requirement  in  any  elementary  biology  syllabus. 
On  the  other  hand  the  attempt  has  been  made  not  to  burden  the 
pupil  with  matter  required  for  advanced  biology  only. 

ACKNOWLEDGMENT 

IN  offering  this  text  book  to  the  public,  recognition  is  due  to 
many  sources  of  aid  and  information. 

The  lists  of  references  appended  to  the  various  chapters  fulfill 
the  double  purpose  of  indicating  some  of  the  authorities  which 
have  been  consulted  and  of  telling  the  student  where  fuller  in- 
formation may  be  obtained. 

The  cuts,  in  so  far  as  they  are  not  original,  are  credited  to  the 
proper  sources  in  each  case.  In  many  cases,  these  are  changed 
in  some  degree,  to  conform  to  the  uses  of  the  text. 

The  author  is  especially  indebted  to  the  cheerful  assistance  of 
his  wife  in  the  laborious  task  of  reading  and  correcting  the  manu- 
script and  proof,  and  to  his  fellow  teacher,  Miss  C.  E.  Reed,* for 
many  helpful  suggestions  as  to  content  and  arrangement. 

If  there  be  aught  of  use  or  value  in  this  book  let  it  be  to  the 
credit  of  the  authorities  consulted  and  the  help  received;  for  its 
many  shortcomings  the  author  alone  is  responsible. 

T.  J.  MOON 


CONTENTS 

PAGE 

CHAPTER  I.  INTRODUCTION 1 

Definition  of  Biology.     Reasons  for  study.     Organic  things.     In- 
organic things.     Familiar  biology. 

CHAPTER  II.  THE  LIKENESS  OF  LIVING  THINGS 5 

Processes  common  to  organic  things. 
CHAPTER  III.  ELEMENTS,  THE  ALPHABET  OF  LIVING  THINGS 9 

Oxygen  and  oxidation.     Occurrence,  properties  and  uses  of  other 

common  elements. 

CHAPTER  IV.  COMPOUNDS,  BIOLOGY'S  BUILDING  MATERIALS 18 

Water;  —  Carbon     dioxide;  —  Proteids;  —  Fats;  —  Carbohydrates; 
—  Method  of  testing. 

CHAPTER  V.  PROTOPLASM,  THE  "Bios"  OF  BIOLOGY 25 

Protoplasm,  its  composition  and  properties.    Cell,  Tissues,  Organs, 
System.     Adaptation. 

CHAPTER  VI.  THE  STRUCTURE  OF  SEEDS 31 

Parts  of  typical  seed.     Bean  and  Corn  seeds  as  examples. 

CHAPTER  VII.   GERMINATION 41 

Conditions  necessary.     Stages  hi  germination.     Corn  and  Bean. 

CHAPTER  VIII.  ROOTS 49 

Characteristics.     Structure.     Functions.    Adaptations. 

CHAPTER  IX.  ABSORPTION  AND  OSMOSIS 58 

Use  of  water  to   plants.     Turgescence.     Osmosis,  definition  and 
essentials  for.     Root  hairs.     Geotropism.    Hydrotropism. 

CHAPTER  X.   STEMS,  THEIR  FORMS  AND  FUNCTIONS 68 

Characteristics.     Functions.     Kinds  of  branching.     Forms  of  stems. 
Buds. 

CHAPTER  XI.   STEM  STRUCTURE 75 

External  structure.    Grafting.    Internal  structure,  dicot.  and  monocot. 
types. 

CHAPTER  XII.  LEAVES  AND  LEAF  STRUCTURE 86 

Functions.     General   structure.     Minute   structure.     Adaptation. 
Modified  forms.     Fall  of  leaves. 

vii 


viii  CONTENTS 

PAGE 

CHAPTER  XIII.  LEAF  FUNCTIONS . .  ^.^ 96 

Photosynthesis.     Digestion.     Assimilation.     Respiration.     Transpi- 
ration. 

CHAPTER  XIV.   FLOWERS:  POLLENATION  AND  FERTILIZATION 108 

Structure  and  function  of  flower  parts.    Adaptations  for  pollenation 
by  wind  and  insects.    Pollen;  Ovule;  Fertilization  stages. 

CHAPTER  XV.  FRUITS  AND  THEIR  USES 118 

Definition;  —  Types  of  fruits;  —  Functions.     Dispersal.     Economic 
importance. 

CHAPTER  XVI.  SPORE-BEARING  PLANTS 127 

Classes  of  plants.    Representatives.    Fungi  as  type  of  spore  plants. 

CHAPTER  XVII.   BACTERIA .' 133 

Kinds.    Method  of  study.    Useful  and  harmful  forms.    Natural  and 
artificial  protection.    Antiseptics.     Disinfectants.    History. 

CHAPTER  XVIII.  PROTOZOA 146 

Relation  to  higher  animals.     Amoeba  and  Paramoecium  as  types. 
Life  functions  compared. 

CHAPTER  XIX.  METAZOA 154 

Development.     Specialization.     Classification. 
CHAPTER  XX.  WORMS 161 

Representatives.     Structure.     Adaptations.     Economic  importance. 

Parasitism.     Earthworm.    Trichina.     Hookworm.    Tapeworm. 

CHAPTER.  XXI.  ARTHROPODS 172 

Characteristics.     Classification.     Scientific  classification  explained. 

CHAPTER  XXII.  CRUSTACEA,  A  CLASS  OF  ARTHROPODS 179 

Characteristics.     Crayfish  as  type.     Structure  and  adaptations  of 
crayfish.    Homology.     Life  history. 

CHAPTER  XXIII.  INSECTS,  A  CLASS  OF  ARTHROPODS 192 

Characteristics.     Grasshopper  as  type.     Structure  of  grasshopper. 
Adaptations.    Life  History.     Economic  importance. 

CHAPTER  XXIV.  INSECTS;  —  BUTTERFLY,  MOTH  AND  BEE 205 

Structure  and  adaptations  of  each.    Communal  life  and  specialization 
of  bee.     Economic  importance. 

CHAPTER  XXV.  INSECTS  AND  DISEASE 220 

Structure  and  Life  History  of  Fly  and  Mosquito.    Relation  to  dis- 
ease;—  how  proven.     Means  of  prevention  and  control. 

CHAPTER  XXVI.  THE  VERTEBRATES 234 

Classification  of  animals.     Development.     Classification  and  types 
of  vertebrates. 


CONTENTS  ix 

PAGE 

CHAPTER  XXVII.  FISHES 239 

Structure,    external    and    internal.      Life    History.      Adaptations. 

Economic  value. 
CHAPTER  XXVIII.  THE  FROG  AND  ITS  RELATIVES.  . .' 252 

Characteristics  of  the  amphibia.     Structure  of  frog.    Adaptations. 
CHAPTER  XXIX.  THE  AMPHIBIA;  —  LIFE  HISTORY  AND  HABITS 267 

Metamorphosis  of  frog.     Toad,  Salamander  and  Frog  compared. 

Economic  importance. 
CHAPTER  XXX.   REPTILES 273 

Representatives.       Characteristics.       Adaptations.       False     ideas. 

Poisonous  snakes.     Treatment. 
CHAPTER  XXXI.   BIRD  STRUCTURE  AND  ADAPTATIONS 281 

Characteristics.     Adaptations  for  flight.     Adaptations  for  active 

life.    Adaptations  of  beaks  and  feet. 
CHAPTER  XXXII.  BIRD  HABITS 294 

Food.     Nesting.     Eggs.     Migration.     Economic  importance. 
CHAPTER  XXXIII.  MAMMALS 310 

Characteristics.     Adaptations  of  limbs,  teeth,  and  body  coverings. 

Special  adaptations  of  rodents,  ungulates,  carnivora  and  primates. 

Man's  place  in  the  group. 
CHAPTER  XXXIV.   THE  DEVELOPMENT  OF  MAN 321 . 

Relation  to  other  animals.     Idea  of  evolution.     Evidences  of  evo- 
lution. 
CHAPTER  XXXV.  THE  METHOD  OF  EVOLUTION 326 

Antiquity  of  the  idea.    Lamarck's    theory.     Darwin  and  Natural 

Selection.     Summary  of  the  theory;  —  its  conclusions. 

CHAPTER  XXXVI.  THE  DEVELOPMENT  OF  CIVILIZED  MAN 333 

Ancient  records.  Primitive  man.  Stages  in  development.  Imple- 
ments used.  Results  of  higher  mentality.  Present  races. 

CHAPTER  XXXVII.   FOOD 342 

Necessity.  Definition.  Functions  of  various  food  stuffs.  Measure- 
ment of  values.  Proportions.  Balanced  ration.  Digestibility. 
Cost.  Cooking.  Lipoid.  Vitamines. 

CHAPTER  XXXVIII.  NUTRITION 363 

Digestive  changes.  Digestive  organs.  Mouth.  Teeth.  Stomach. 
Intestine.  Glands.  Absorption.  Assimilation. 

CHAPTER  XXXIX.   RESPIRATION 382 

Development  of  organs,  in  lower  forms.  Structure  and  adaptation 
of  nose,  trachea,  lungs,  diaphragm.  Changes  in  air  and  blood.  Venti- 
lation. 

CHAPTER  XL.   CIRCULATION 392 

Function.  Blood,  its  composition  and  use.  Heart.  Arteries,  Veins, 
Capillaries.  Lymph  circulation. 


x  CONTENTS      •. 

PAGE 

CHAPTER  XLI.  EXCRETION 403 

Source  of  waste.    Organs  of  excretion.    Kidneys,  Lungs,  Skin.    Heat 
regulation. 

CHAPTER  XLII.  THE  NERVOUS  SYSTEM 408 

Location  and  functions  of  cerebrum,  cerebellum,  medulla, .  spinal 
cord,  sympathetic  system.    Regions  of  control  for  various  activities. 

CHAPTER  XLIII.  THE  SENSE  ORGANS 415 

Irritability.     Touch.     Taste.     Smell.     Hearing,   structure  of  ear, 
care  of  ears.     Sight,  structure  of  eye,  care  of  eyes. 

CHAPTER  XLIV.  BIOLOGY  ,AND  HEALTH 425 

Hygiene  of  Muscles,  of  Digestion,  Breathing.     Bathing.     Care  of 
eyes,  teeth,  feet.     Posture.     Sleep. 

CHAPTER  XLV.  Civic  BIOLOGY 440 

Food  control.    Sanitation.    Disease  prevention.    Housing  conditions. 
Food  laws.     Medicines. 

CHAPTER  XL VI.  ECONOMIC  BIOLOGY  OF  PLANTS 446 

General  uses.    Harmful  forms.     Plant  uses  in  detail. 

CHAPTER  XLVII.  ECONOMIC  BIOLOGY  OF  INVERTEBRATES 467 

General  uses  of  animals.  •  Harmful   forms.     Importance  of  each 
group  in  detail.    Harmful  insects  and  their  treatment. 

CHAPTER  XL VIII.  ECONOMIC  BIOLOGY  OF  VERTEBRATES 480 

Fish.     Amphibia.     Reptiles.     Birds.     Mammals. 
CHAPTER  XLIX.  BIOLOGY  AND  AGRICULTURE 486 

Soil  formation.    Plant  breeding  and  protection.    Animal  husbandry. 

Bacteria  on  the  farm. 
CHAPTER  L.  ECONOMIC  IMPORTANCE  OF  FORESTS 495 

Value  of  forests.    Enemies  of  forests.    Protection.    Timber  structure. 

Street  trees. 
CHAPTER  LI.  TOBACCO  AND  TABLE  BEVERAGES  .  508 

Tobacco,  physical  and  social  objections  to  its  use.     Tea,  Coffee, 

Cocoa,  and  Chocolate. 
CHAPTER  LII.  ALCOHOL  IN  RELATION  TO  BIOLOGY  . .  514 

Composition  and  kinds  of  alcoholic  liquors.    Physical  effects.    Not 

a  food.    Alcohol  and  disease.    Waste  of  resources. 
CHAPTER  LIII.  SOME  GENERAL  BIOLOGIC  PROCESSES  .  .  524 

Osmosis  in  life  processes.    Oxidation.    Circles  in  Nature.    Evolution 

of  life  functions. 
CHAPTER  LIV.  HISTORICAL  DEVELOPMENT  OF  BIOLOGY  . . 

Biologic  development.    The  work  of  Pasteur,  Roux,  von  Behring, 

Lister,  Carrell,  Flexner.     Darwin,  Huxley,  Mendel,  Burbank. 

INDEX..  •• 549 


BIOLOGY    FOR    BEGINNERS 


CHAPTER  I 

INTRODUCTION 

The  student  should  make  sure  that  he  understands  every  term  used  in  his 
Biology  lessons.  This  book  will  include  vocabularies  like  the  following,  but 
in  addition,  a  good  dictionary  should  be  consulted  frequently  and  derivations 
studied.  As  is  shown  in  the  first  paragraph  on  this  page,  a  great  deal  can 
be  learned  about  the  meanings  of  scientific  terms  by  looking  up  their  deri- 
vations. 

Vocabulary 

Domestic,  tamed,  as  applied  to  animals  and  plants  used  by  man. 
Biology,  the  science  of  living  things. 
Organic,  pertaining  to  living  things. 
Inorganic,  things  which  have  never  been  alive. 

Biology  is  a  study  of  living  things.  The  dictionary  tells  us  that 
this  term  comes  from  two  Greek  words,  "  Bios  "  which  means 
"  life,"  or  "  living  things,"  and  "  ology,"  a  word-ending  meaning 
"  the  science  or  study  of."  The  two  parts  thus  make  a  perfect 
definition  of  biology,  which  is,  truly,  "  The  science  of  living  things." 

Classes  of  Things.  All  things  in  the  world  can  be  divided  into 
two  classes;  those  which  are,  or  have  been  alive,  and  those  which 
have  never  lived.  The  former  are  called  organic  substances,  and 
the  latter  inorganic. 

Organic  things  include  both  plants  and  animals,  together  with 
all  substances  derived  from  them.  Inorganic  things  include  the 
members  of  the  mineral  kingdom  such  as  stone,  glass,  or  iron,  as 
well  as  water,  carbon  dioxide,  oxygen  and  similar  substances. 
Biology  is  the  science  which  deals  with  the  study  of  organic  things, 
as  its  derivation  shows. 

Words  as  Tools.  Since  three  new  words  have  been  used  already 
—  biology,  organic,  and  inorganic  —  it  may  appear  that  the  subject 

1 


BIOLOGY  FOR  BEGINNERS 


"is  to  :be  -made  -diffieuk  because  of  many  hard  and  strange  terms. 
There  need  be  no  alarm  at  the  prospect  if  we  will  consider  each 
new  word  as  a  tool  which  will  enable  us  to  do  our  work  better, 
more  accurately,  and  more  easily. 

It  is  simpler  to  say  "  organic  substances  "  than  to  say,  "  sub- 
stances which  are  or  have  been  alive."  It  is  also  more  accurate, 
and  furthermore  we  have  increased  our  vocabulary  by  the  addition 
of  this  new  tool. 

We  should  think  a  carpenter  very  foolish  who  cut  all  his  lumber 
with  a  jack  knife  because  he  thought  it  too  much  trouble  to  learn 
to  use  a  saw.  Students  in  their  school  life  are  workmen,  and  their 
most  important  tools  are  words.  Each  subject  taken  up,  like 
different  kinds  of  carpenter  work,  requires  the  use  of  a  certain 
number  of  new  tools  (words).  These  must  be  learned  before 
the  student  can  do  his  work  efficiently. 

On  the  other  hand  a  carpenter  would  be  foolish  to  load  up  his 
chest  with  a  lot  of  tools  which  he  rarely  used,  and  so,  in  our  study, 
we  have  included  only  those  new  names  and  terms  without  which 
we  could  not  possibly  get  along.  If  we  learn  to  use  them,  we  will 
not  have  to  "  cut  off  our  board  with  a  jack  knife." 

Sciences  Included  in  Biology.  .  Although  biology  is  a  single  and 
closely  united  science  based  on  the  study  of  all  things  that  are  or 
have  been  alive,  it  is  so  broad  in  scope  that  it  includes  many 
special  branches. 

Some  of  these  are  already  familiar,  such  as  botany,  which  deals 
with  plants;  zoology,  which  deals  with  animals;  hygiene,  which 
concerns  the  care  of  the  human  body;  physiology,  which  is  the 
science  of  the  use  or  function  of  living  organs;  and  many  others. 

Familiar  Biology.  To  begin  with,  each  one  of  us  has  studied 
biology  already  by  observing  the  things  of  nature  about  us.  Is 
this  not  true?  We  know  some  plants  and  trees  by  name.  We 
know  how  to  cultivate  gardens,  what  will  help  plants  grow,  the 
names  of  many  flowers.  All  of  us  buy  and  use  fruits,  grain,  and 
vegetables.  We  also  know  something  about  the  care  of  animals, 
and,  most  important  of  all,  are  anxious  to  learn  all  that  we  can 
about  the  care  and  use  of  our  own  bodies. 


INTRODUCTION  3 

Reasons  for  the  Study  of  Biology.  Biology  is  a  required  study 
in  many  schools,  and  we  have  a  right  to  ask  why  it  is  considered 
so  important  that  we  are  obliged  to  study  it. 

In  the  first  place  there  are  few  subjects  that  add  so  much  to 
ANIMAL 


PLANT  . 

FIG.  1.    Diagram  to  show  the  relation  of  General  Biology  to  the  biological 
sciences.     From  Calkins. 

general  culture  by  increasing  the  number  of  things  in  which  we. 
are  interested  and  about  which  we  should  have  information. 

Few  people  really  see  very  much  of  the  things  about  them  — 
accurate  observation  is  a  very  rare  but  valuable  trait,  and  biology 
will  greatly  increase  the  powers  of  observation. 


4  BIOLOGY  FOR  BEGINNERS 

Mere  observation  of  facts  is  not  enough,  however,  for  one  should 
be  able  to  draw  correct  conclusions  from  what  he  sees.  This 
ability  to  think  and  reason  is  one  of  the  chief  aims  of  the  laboratory 
work  in  biology  or  any  other  science. 

Although  these  reasons  for  the  study  of  biology  are  by  far  the 
most  important,  others  can  be  mentioned  which  may  seem  more 
practical.  Tt  is  the  foundation  of  farming,  gardening,  and  forestry 
and  upon  its  laws  are  based  the  care  and  breeding  of  all  domestic 
animals  and  plants. 

In  even  a  more  personal  way,  biology  deals  with  the  health 
and  care  of  our  own  bodies  —  hygiene.  It  also  includes  the  study 
of  the  cause  and  prevention  of  disease,  the  work  of  bacteria,  and 
means  of  maintaining  healthful  surroundings  —  sanitation. 

One-half  of  all  human  deaths  are  caused  by  germ  diseases  and 
at  least  half  of  these  could  be  prevented  by  proper  knowledge 
and  practice  of  hygiene  and  sanitation.  This  in  itself  is  sufficient 
reason  for  interest  in  the  study  of  biology. 

SUMMARY 

Biology,  a  study  of  living  things. 

1.  Derivation:    Bios,  Logos. 

2.  Definition. 

3.  Classes  of  things. 

Inorganic  (meaning  and  examples). 
Organic  (meaning  and  examples). 

Plants: 

Animals. 

4.  Words  as  tools. 

5.  Sciences  included. 

6.  Familiar  biology. 

7.  Reasons  for  study. 

Adds  to  culture. 

Cultivates  power  of  observation. 
Teaches  to  think  and  reason. 
Importance  in  many  industries. 
Relation  to  health. 

Hygiene. 

Sanitation. 


CHAPTER  II 

THE   LIKENESS   OF   ALL  LIVING  THINGS 

Vocabulary 

Similarity,  likeness. 

Assimilation, "  to  be  made  the  same,"  that  is,  the  process  by 
which  food  stuff  is  made  into  tissue. 

Nutrition,  all  the  processes  by  which  food  is  prepared  and  assimi- 
lated in  the  body. 

Excretion,  the  passing  off  of  waste  matter  from  plant  or  animal. 

Biology,  then,  is  the  study  of  organic,  or  living  things,  and 
living  things  include  both  plants  and  animals.  At  first  one  would 
say  that  plants  and  animals  have  very  little  similarity  and  that  it 
would  be  difficult  to  study  them  together,  but  let  us  see  if  this 
is  true. 

Nutrition.  First,  both  plants  and  animals  are  alive  and  grow 
in  size  and  that  means  that  they  both  need  food.  A  cat,  for  instance, 
has  to  eat,  and  a  geranium  has  to  have  earth,  in  order  to  live.  The 
cat  uses  organic  food  and  the  plant  inorganic.  The  cat  obtains 
its  food  by  means  of  its  claws  and  teeth,  while  the  food-getting 
of  the  plant  is  done  largely  by  the  roots.  They  are  both  dependent 
on  food. 

After  they  get  their  food,  both  plants  and  animals  have  to  put 
it  into  liquid  form  in  their  bodies.  We  call  that  process  digestion. 
Then  the  digested  food  undergoes  a  change  by  which  the  milk  or 
meat  actually  becomes  part  of  the  cat,  while  the  plant  foods  be- 
come part  of  the  geranium.  This  is  a  very  wonderful  process  and 
is  called  assimilation.  (Look  up  this  word  in  the  dictionary  and 
see  if  you  can  tell  why  it  is  used  in  this  way.) 

Food-getting,  digestion,  and  assimilation  together  make  up  the 
process  of  nutrition  (getting  nourishment).  The  animal  and  the 
plant  have  this  process  in  common. 

5 


6  BIOLOGY  FOR  BEGINNERS 

Respiration.  Another  point  in  which  our  two  examples  are  alike 
is  that  they  both  breathe.  If  we  keep  either  one  in  an  air-tight 
box  it  will  die.  The  cat  breathes  by  means  of  its  lungs  and  it  is 
easy  to  see  the  muscular  movements  involved.  The  leaves  of  the 
plant  breathe  too,  although  our  eyes  cannot  detect  the  way  in 
which  this  is  done.  The  process  of  breathing  is  called  respiration 
in  both  cases. 

Excretion.  Both  cat  and  geranium  use  the  food  that  they 
assimilate  to  build  up  their  bodies  or  to  give  them  energy,  and 
both  throw  off  from  their  bodies  unused  and  changed  food  materials 
by  a  process  called  excretion.  The  animal  does  this  by  means  of 
the  lungs,  skin,  intestines  and  kidneys;  the  plant  by  means  of 
the  leaves. 

Motion.  Another  way  in  which  all  living  things  are  alike  is  in 
the  power  of  motion.  It  is  easy  to  see  the  cat  move,  but  few  observe 
how  the  geranium  turns  its  leaves  to  the  light  and  its  roots  to  the 
water.  Though  animals  usually  have  greater  freedom  of  motion, 
plants  do  not  lack  it  altogether. 

Sensation.  In  a  general  way,  all  plants  and  animals  have  the 
power  of  responding  to  touch,  heat,  light,  and  other  forces  outside 
of  themselves.  This  is  sensation,  and  may  vary  in  its  expression, 
from  the  mere  turning  of  leaves  toward  light  to  the  delicate  opera- 
tion of  a  wonderful  sense  organ  like  the  human  eye. 

Reproduction.  Both  plants  and  animals  reproduce  others  like 
themselves.  Kittens  are  born  and  grow  to  be  cats,  and  the  plant 
bears  seeds  which  will  produce  other  plants  like  itself.  By  this 
wonderful  provision  of  nature,  although  all  organic  things  die, 
others  like  them  are  left  to  take  their  places.  The  processes  of 
reproduction  and  nutrition  are  the  two  most  important  charac- 
teristics of  all  living  things. 

Likeness  of  all  Living  (Organic)  Things.  The  cat  before  the 
fire  and  the  geranium  on  the  window  sill,  though  apparently 
different,  are  really  alike  in  all  of  the  necessary  processes  of  life. 
It  is,  therefore,  possible  and  easy  to  study  plants  and  animals 
together.  Biology  is  not  merely  botany  plus  zoology,  but  a  study 
of  the  life  processes  of  all  living  things. 


THE  LIKENESS  OF  ALL  LIVING  THINGS  7 

Difference  from  Inorganic  Things.  The  points,  in  which  all 
living  or  organic  things  are  alike,  are  also  the  points  in  which  they 
differ  from  inorganic  things.  A  stone  and  a  piece  of  iron  are 
familiar  examples  of  inorganic  matter.  We  cannot  imagine  a  stone 
taking  food  or  growing,  or  a  piece  of  iron  moving  or  reproducing 
its  kind.  Our  study  of  biology  is  thus  sharply  separated  from 
inorganic  things. 

To  be  sure,  plants  can  take  inorganic  matter  and  by  certain 
wonderful  processes  make  it  into  the  living  plant  as  we  have 
mentioned.  But  it  then  ceases  to  be  inorganic  and  becomes  a 
part  of  the  plant.  Plant  and  animal  are  alike  in  all  essential  ways 
and  they  also  differ  in  these  ways  from  all  inorganic  substances. 


SUMMARY 
Organic  things  (Plant  and  Animal). 

1.  Live,  grow,  and  move. 

2.  Obtain  food. 

3.  Digest  and  absorb  food. 

4.  Assimilate  food  as  part  of  themselves. 

5.  Excrete  waste. 

6.  Reproduce. 

Inorganic  things  can  perform  none  of  the  above  processes. 

Organic  and  Inorganic  things  resemble  each  other  in  the  following  points: 

1.  They  are  composed  of  similar  elements. 

2.  They  contain,  use  and  produce  similar  compounds,  such  as  carbon 

dioxide,  water,  etc. 

3.  They  have  characteristic  shapes  and  weights. 

4.  They  undergo  chemical  changes. 

5.  They  liberate  energy. 

Organic  things  differ  from  Inorganic,  in  the  following  points: 

1.  They  have  organs  for  various  functions. 

2.  They  are  composed  of  cells. 

3.  They  always  contain  protoplasm. 

4.  Their  growth  is  from  within. 

5.  They  respond  to  their  surroundings  (irritability). 

6.  They  follow  a  "  life  cycle." 

7.  They  depend  upon  oxidation  for  life. 


BIOLOGY  FOR  BEGINNERS 

PROCESSES  IN  WHICH  ORGANIC  THINGS  ARE  ALIKE 


Process 

i 
In  plants  is  per- 
formed by 

In  animals  is  per- 
formed by 

Food-getting 

Roots,  leaves 

Teeth,  claws,  etc. 

Digestion 

Ferments  in  the  tissues 

Stomach,     intestines, 

glands,  etc. 

Absorption 

All  live  tissues 

Intestine,  stomach,  etc. 

Assimilation 

«  •        U                 « 

All  live  tissues 

Respiration  (oxidation) 

Air  spaces  and  tissues 

Lungs,    gills,    etc.,    all 

tissues 

Excretion 

Leaves 

Kidneys,  skin,  etc. 

Motion 

Flowers,    leaves,    ten- 

Legs, wings,  fins,  etc. 

drils,  etc. 

Sensation 

Leaves,  tendrils 

Nerves,  sense  organs 

Reproduction 

Seeds,  slips,  etc. 

Eggs,  live  young 

What  evidences  can  you  give  of  any  of  these  processes,  in  either 
plants  or  animals? 

Since  both  plants  and  animals  perform  similar  processes,  what 
might  you  expect  about  the  stuff  they  are  made  of? 


COLLATERAL   READING 

General  Biology,  Sedgwick  and  Wilson,  pp.  1-19;  Applied  Biology, 
Bigelow,  pp.  10-22,  122-132;  Practical  Biology,  Smallwood,  pp.  1-10; 
Essentials  of  Biology,  Hunter,  pp.  26-30;  Elementary  Zoology,  Galloway, 
pp.  36-54,  72-97;  Biology,  Calkins,  pp.  6-15;  General  Zoology,  Pearse, 
pp.  25-36. 


CHAPTER  III 

ELEMENTS,  THE  ALPHABET  OF  ALL  LIVING  THINGS 

Vocabulary 
Individual,  separate. 
Innumerable,  very  many. 

Oxidation,  the  union  of  any  thing  with  oxygen. 
Combustion,  rapid  oxidation,  producing  light  and  heat. 
Restrain,  to  hold  back. 

All  the  words  of  our  language  are  made  from  less  than  thirty 
letters.  If  we  think  of  our  big  dictionaries  we  realize  what  an 
enormous  number  of  different  combinations  can  be  formed  from 
a  few  letters. 

Elements  and  Compounds.  In  something  the  same  way,  all 
the  matter  in  the  world  is  composed  of  about  eighty  individual 
substances  called  elements.  These  we  might  think  of  as  the  letters 
in  a  chemical  alphabet  which  spell  all  the  substances  —  both 
organic  and  inorganic  —  that  are  in  existence.  When  elements 
unite,  they  form  all  the  innumerable  things  that  compose  the 
world  around  us.  -These  substances,  formed  by  the  union  of  two 
or  more  elements,  are  called  compounds.  For  example,  iron  is  an 
element.  Oxygen  in  the  air  is  also  an  element.  When  these  two 
unite,  they  form  a  compound  which  we  call  iron  rust. 

Organic  substances  utilize  only  about  ten  elements,  but  when 
we  stop  to  think  of  the  thousands  of  kinds  of  plants  and  of  animals, 
and  of  all  the  different  substances  of  which  they  are  made,  we  see 
that  ten  elements  are  enough  to  make  a  wide  variety  of  compounds. 

What  to  Learn  about  Them.  The  complete  study  of  these 
elements  and  their  compounds  is  called  chemistry,  but  for  the 
present  we  need  to  learn  only  four  things  about  the  elements 
which  compose  organic  substances:  (1)  their  names,  (2)  where 

9 


10  BIOLOGY  FOR  BEGINNERS 

they  are  found,  (3)  enough  of  their  characteristics  or  properties 
so  that  we  can  recognize  them,  and  (4)  their  use  to  living  things. 

OXYGEN 

Where  it  is  Found.  We  already  know  that  oxygen  (O)  is  part 
of  the  air,  but  it  is  also  a  part  of  water,  sand,  soil,  rock,  and  many 
other  things.  It  may  be  hard  to  understand  how  a  gas,  like  oxygen, 
can  be  a  part  of  a  liquid,  like  water,  or  of  a  solid  like  wood,  but 
this  is  true.  Oxygen  is  found  in  all  plant  and  animal  substance. 
In  fact  it  is  the  most  abundant  element  in  the  world,  and  is  itself 
one-half  of  the  solid  material  of  the  earth. 

Properties.  We  shall  see  oxygen  prepared  in  the  laboratory,  and 
shall  discover  that  it  is  a  colorless,  odorless,  and  tasteless  gas.  It 
is  heavier  than  air,  will  dissolve  slightly  in  water,  and  most  curious 
of  all,  though  it  will  not  burn,  it  nevertheless  makes  other  things 
burn  very  rapidly.  Iron,  copper,  and  many  other  substances 
which  do  not  seem  to  burn  at  all  in  the  air  will  do  so  in  oxygen, 
while  sulphur  and  wood,  which  do  burn  in  air,  burn  very  fast  in 
oxygen. 

Test.  It  is  the  only  substance  which  will  cause  a  glowing  splinter 
to  burst  into  flame.  This  fact  is  utilized  in  testing  whether  a  gas 
is  oxygen  or  not,  and  is  therefore  called  a  test  for  oxygen. 

Oxidation.  When  anything  unites  with  oxygen,  the  process  is 
called  oxidation,  and  the  compound  formed  by  the  substance  and 
the  oxygen  is  called  an  oxide. 

Oxygen  may  unite  with  substances  rapidly,  as  when  a  stick 
burns,  or  slowly,  as  when  iron  rusts.  An  oxide  is  always  the  product, 
and  there  is  always  a  more  important  product,  namely,  heat  energy. 

Both  plants  and  animals  use  oxygen.  Heat  energy  is  necessary 
for  all  life.  All  plants  and  animals  therefore  depend  on  oxygen 
which  they  take  into  their  bodies  by  breathing,  as  we  have  seen 
in  CKapter  II.  As  the  living  tissues  become  oxidized  they  produce 
heat  and  energy,  leaving  a  residue  of  oxides  and  other  material  to 
be  thrown  off  as  waste.  The  food  assimilated  as  tissue  contains 
the  vital  energy  which  oxidation  releases. 


THE  ALPHABET  OF  ALL  LIVING  THINGS 


11 


Live  and  Dead  Engines.  A  living  organism  is  often  compared 
to  a  steam  engine.  Both  need  a  supply  of  food  (fuel),  and  both 
must  have  oxygen  to  unite  with  (oxidize)  the  food  and  set  free 
its  energy.  In  both,  heat  is  produced  by  this  oxidation  and  then 
changed  into  motion,  and  in  both  there  are  waste  products  which 
have  to  be  removed. 

But  an  engine  is  only  an  inorganic  thing.  It  cannot  get"  its 
own  food,  it  does  not  assimilate  or  grow,  it  does  not  excrete  its 
waste  products,  or  reproduce.  Really  the  only  way  in  which  it 
resembles  a  living  thing  is  that  it  depends  on  energy  which  is 
released  from  substances  by  uniting  with  oxygen,  and  turns  this 
energy  into  motion. 

RESEMBLANCES 


A  living  organism 

A  steam  engine 

Requires 

Food 

Fuel 

To  unite  with 

Oxygen 

Oxygen 

By  means  of 

Respiration 

Draft 

To  produce 

Heat  and  energy 

Heat  and  energy 

Leaving  waste 

Unused  food 

Ashes 

Carbon     dioxide     (in 

Carbon  dioxide  (in  chim- 

breath) 

ney  gas) 

DIFFERENCES 


A  living  organism    . 

A  steam  engine 

Is  alive 
Grows  in  size 
Repairs  wear 
Reproduces 

Is  not  alive 
Does  not  grow 
Wears  out 
Cannot  reproduce 

Similarities  based  on  oxidation,  differences  based  on  functions  of  the 
protoplasm. 

Other  Uses  of  Oxygen.  Oxygen  has  many  other  uses  in  nature. 
It  causes  combustion  from  which  we  get  heat  and  power.  It  also 
causes  rusting,  oxidation,  and  decay.  Its  myriad  compounds  are 


12  BIOLOGY  FOR  BEGINNERS 

absolutely  necessary  as  food  and  drink.  But  its  chief  importance 
in  biology  is  that,  by  uniting  with  the  substance  of  both  plant 
and  animal,  it  sets  free  the  energy  which  keeps  them  alive.  Without 
oxygen,  no  life  can  exist. 

NITROGEN 

Where  it  is  Found.  Nitrogen  (N)  is  another  important  element. 
It  makes  up  four-fifths  of  the  air.  It  is  found  combined  with  several 
minerals  in  the  soil  and  exists  in  the  living  tissue  of  all  organic 
things. 

Properties.  Nitrogen  resembles  oxygen  in  being  colorless,  odor- 
less, and  tasteless,  and  in  that  it  will  not  burn.  It  is  less  soluble 
in  water  and  lighter  in  weight.  It  is  the  exact  opposite  of  oxygen 
in  its  behavior,  for  it  will  not  cause  combustion,  nor  will  it  combine 
readily  with  other  elements.  Its  compounds  decompose  easily. 

Uses.  It  is  found  in  the  active  living  substance  of  all  plants 
and  animals  and  is  essential  to  their  life.  Its  various  compounds 
are  our  most  necessary  foods. 

All  fertilizers  which  we  use  for  plants,  as  well  as  meat,  milk, 
eggs,  and  many  other  animal  foods  contain  very  important  com- 
pounds of  nitrogen. 

If  the  air  were  pure  oxygen,  fires  could  not  be  controlled  and 
things  would  oxidize  too  rapidly.  Thus,  another  important  use  of 
nitrogen  is  to  restrain  the  activity  of  oxygen  and  make  the  at- 
mosphere suitable  for  life. 

HYDROGEN 

Where  it  is  Found.  Hydrogen  (H)  occurs  combined  in  water, 
plant  and  animal  tissue,  wood,  coal,  gas,  and  all  acids. 

Properties.  It  resembles  both  nitrogen  and  oxygen  in  being 
colorless,  odorless,  and  tasteless.  It  does  not  dissolve  much  in 
water  and  it  will  not  cause  things  to  burn,  but  unlike  either  nitrogen 
or  oxygen  it  burns  readily  and  even  explodes  when  mixed  with  air 
and  brought  into  contact  with  fire.  It  is  the  lightest  substance 
known  and,  because  of  this  fact,  is  used  to  fill  balloons. 


THE  ALPHABET  OF   ALL  LIVING   THINGS  13 

Uses.  Hydrogen  is  important  to  the  biologist  because  it  unites 
readily  with  oxygen  and  forms  water.  It  also  combines  with  both 
oxygen  and  carbon  (another  element)  and  forms  a  whole  series  of 
compounds  called  fats,  sugars,  and  starches.  It  is  an  essential 
ingredient  in  all  organic  tissue. 

CARBON 

Carbon  (C)  is  an  element  with  which  we  are  more  familiar;  coal, 
charcoal,  and  wood  are  common  forms.  Lead-pencils  do  not 
really  contain  lead  at  all  but  another  form  of  carbon  called 
graphite.  Strangest  of  all,  the  diamond  is  carbon,  too,  though 
not  a  common  form. 

Properties.  Carbon  is  (except  in  the  diamond)  a  black  solid, 
not  soluble  in  any  thing.  At  ordinary  temperature  it  is  very 
inactive.  When  heated,  however,  it  unites  readily  with  oxygen, 
(that  is,  it  burns)  and  forms  an  oxide  which  is  called  carbon  dioxide 
—  a  compound  very  necessary  to  plants,  as  we  shall  see  later. 

Uses.  Carbon's  importance  to  biology  is  due  to  the  fact  that  it 
is  a  part  of  all  organic  substances,  combining  with  hydrogen, 
nitrogen,  and  oxygen  and  other  elements  to  form  all  plant  and 
animal  tissues  and  many  of  their  foods. 

We  know  that  if  any  plant  or  animal  substance  is  partly  burned 
a  black  solid  is  produced.  This,  in  every  case,  is  carbon.  We  also 
know  that  if  the  burning  is  continued  the  carbon  will  disappear. 
This  means  that  it  becomes  oxidized  into  carbon  dioxide,  which  is 
an  invisible  gas. 

Plants  alone  have  •  the  power  to  obtain  their  carbon  from  the 
carbon  dioxide  of  the  air.  Animals  depend  entirely  on  plant 
foods  for  the  carbon  compounds  which  are  necessary  for  their  life. 

SULPHUR 

Sulphur  (S)  is  a  yellow  solid  element,  which  (like  carbon)  will 
not  dissolve  in  water,  but  can  be  dissolved  in  other  chemicals. 

Sulphur  itself  has  no  odor,  but  it  readily  unites  with  oxygen, 
even  at  low  temperatures.  It  also  burns  readily,  producing  in 


14  BIOLOGY  FOR  BEGINNERS 

both  cases  an  oxide  of  sulphur  (SO2)  with  the  familiar,  suffocating 
odor  which  we  wrongly  associate  with  sulphur  itself. 

Its  importance  in  biology  is  due  to  the  fact  that  it  is  a  part  of 
the  living  substance  of  all  organic  things  though  in  smaller  amounts 
than  any  of  the  preceding  elements. 

Mustard,  onions,  and  eggs  will  blacken  silver  dishes.  This  is 
due  to  the  sulphur  compounds  which  they  contain;  but  sulphur, 
in  smaller  quantities,  is  found  hi  all  plants  and  animals. 


PHOSPHORUS 

Phosphorus  (P)  is  a  light  yellow,  waxy,  solid  element.  Like 
sulphur,  it  dissolves  in  several  other  liquids,  but  not  in  water. 

It  also  resembles  sulphur  in  that  it  unites  readily  with  oxygen. 
In  fact  it  unites  with  oxygen  more  readily  than  does  sulphur,  for, 
if  exposed  to  air,  it  will  take  fire  and  burn  fiercely,  forming  an 
oxide  of  phosphorus.  It  has  to  be  kept  covered  with  water  to 
prevent  it  from  burning  and  is  a  dangerous  and  poisonous  element. 

It  seems  strange  that  such  a  substance  should  be  a  necessary 
ingredient  of  our  bodies  and,  in  fact,  of  all  living  things.  To  be 
sure  it  is  present  in  small  amount  but  is  absolutely  essential, 
being  especially  abundant  in  bone  and  nerve  tissue. 

You  have  probably  heard  plant  fertilizers  called  "  phosphates." 
This  is  because  they  contain  phosphorus  compounds. 


IRON 

Iron  is  another  element.  We  are  familiar  with  it  as  a  heavy, 
solid  metal;  and  we  know  it  unites  slowly  with  oxygen  forming 
iron  oxide  (rust).  This  is  about  the  last  thing  we  would  think  to 
be  of  use  in  the  bodies  of  plants  or  animals.  However,  iron  is 
absolutely  necessary  in  the  green  coloring  matter  of  plants  and  in 
the  red  blood  of  animals.  Later  we  will  learn  the  remarkable 
services  which  its  compounds  perform  in  these  substances. 


THE  ALPHABET  OF  ALL  LIVING  THINGS  15 

SODIUM,  POTASSIUM,  AND  CALCIUM 

Our  list  of  elements  important  to  organic  life  will  end  with  three 
similar  ones  —  sodium,  potassium,  and  calcium.  These  are  light, 
metallic  substances  which  burn  when  put  in  water  and  are  there- 
fore very  dangerous  to  handle.  Potassium  compounds  must  be 
in  the  soil  if  plants  are  to  thrive,  while  sodium  and  calcium  com- 
pounds are  necessary  for  the  blood  and  skeleton  of  animals. 

Nitrogen,  sulphur,  phosphorus,  iron,  sodium,  potassium,  and 
calcium  are  all  obtained  from  their  mineral  compounds  in  the  soil; 
animals  use  salt  (a  sodium  compound)  directly,  while  they  get 
the  other  elements  from  plant  foods.  Plants  in  turn  obtain  them 
from  the  soil. 

By  themselves,  all  these  elements  are  inorganic  substances,  but 
in  the  wonderful  process  of  assimilation,  plants  and  animals  can 
combine  them  to  form  the  living  stuff  of  which  their  tissues  are 
made.  On  the  other  hand,  by  the  processes  of  oxidation,  death, 
and  decay,  the  complex  organic  compounds  are  broken  up  into 
simpler  forms,  and  return  to  the  soil  or  air  as  inorganic  compounds 
or  elements,  to  be  used  over  again  by  organic  things. 

Here  is  an  estimate  of  the  composition  of  the  human  body, 
which  may  give  an  idea  of  the  comparative  amounts  of  the  different 
elements  in  animal  tissue. 


16 


BIOLOGY   FOR  BEGINNERS 


A  person  weighing  154  pounds  would  be  composed  of; 

Oxygen         97.2    pounds 

Carbon         31.1  " 
Hydrogen     15.2 

Nitrogen        3.8  " 
Calcium         3.8 

Phosphorus    1.75  " 

Sulphur  .27  " 

Chlorine  .25  " 

Fluorine  .22  " 

Potassium        .18  " 

Sodium  .16  " 

Magnesium      .11  " 

Iron  .01  " 


Oxygon     97.2 


Carbon     31.1 


Hydrogen 
15.2 


Nitro- 
gen 
3.8 


a  Iron      .01 
D  Magnesium      .11 
D  Sodium     .16 
D  Potassium      .18 
D  Fluorine      .22 
Chlorine      .25 


Phosphorui 
1.75 


Calcium 
3.8 


FIG.  2.    Elements  composing  a  human  body  weighing  154  pounds.    (Figures 
express  pounds.) 

COLLATERAL   READING 

See  index  of  any  text  book  in  Elementary  Chemistry.  Applied  Biology, 
Bigelow,  pp.  5-9;  Elementary  Biology,  Peabody  and  Hunt,  pp.  5-13; 
Essentials  of  Biology,  Hunter,  pp.  17-25. 


THE  ALPHABET  OF  ALL  LIVING  THINGS 


17 


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CHAPTER  IV 

COMPOUNDS,   BIOLOGY'S  BUILDING   MATERIALS 

Vocabulary 

Extinguish,  to  "put  out"  a  flame. 

Constitutes,  composes. 

Converted,  changed. 

Emergencies,  sudden  needs. 

Distinguish,  to  show  differences  between. 

Characteristics,  properties  by  which  a  substance  may  be  known. 

We  have  learned  the  names  and  something  about  the  charac- 
teristics of  a  few  of  the  elements.  In  dealing  with  these  elements 
and  their  compounds  it  is  necessary  to  find  some  way  to  distinguish 
one  from  another,  in  order  that  they  may  be  properly  studied. 

Method  of  "  Testing  "  Substances.  Such  means  of  distinguish- 
ing are  called  "  tests  "  and  we  have  already  referred  to  one  in  the 
case  of  oxygen.  The  test  consisted  in  the  fact  tha,t  oxygen,  and 
no  other  substance,  would  cause  a  glowing  spark  to  burst  into  flame. 

Before  taking  up  any  test  three  things  must  be  considered. 

1.  A  substance  known  to  be  the  one  we  are  studying  must  be 
tested,  so  that  we  may  know  the  correct  result,  and  be  able  to 
recognize  it  in  an  unknown  case. 

2.  The  test  must  be  true  of  the  substance  sought,  and  of  no 
other.    You  can  readily  see,  that  if  even  one  other  gas  would  kindle 
the  glowing  splinter,  then  that  could  not  be  used  as  a  test  for  oxygen. 

3.  The  test  must  be  made  in  the  same  way,  every  time,  or  else 
one  might  suppose  that  the  result  was  affected  by  the  difference 
in  treatment. 

INORGANIC  COMPOUNDS 

Carbon  Dioxide.  When  carbon  unites  with  oxygen,  it  forms  a 
colorless,  odorless,  and  tasteless  gas  called  carbon  dioxide  (CO 2), 
which  is  heavier  than  air  and  will  extinguish  a  flame. 

18 


BIOLOGY'S  BUILDING  MATERIALS  19 

Carbon  dioxide  is  like  nitrogen  in  many  ways  (mention  them), 
but  if  it  be  mixed  with  lime  water,  it  causes  the  clear  liquid  to  be- 
come milky,  while  nitrogen  does  not.  This  is  the  test  for  carbon 
dioxide. 

Carbon  dioxide  is  a  plant  food;  plants  having  the  power  to 
take  this  gas  from  the  air,  combine  it  with  water,  and  make  it 
into  their  tissues  —  in  fact  it  is  from  this  source  that  all  organic 
carbon  comes. 

Water.  When  hydrogen  combines  with  oxygen,  water  (H^O)  is 
formed  as  we  found  when  studying  hydrogen.  This  compound  is 
so  familiar  that  we  do  not  need  to  learn  any  test  for  its  presence. 
It  may  be  well  to  realize,  however,  that  water  constitutes  much 
over  half  the  weight  of  all  organic  matter;  that  it  is  absolutely 
essential  to  all  life;  and  that  it  is  not  only  a  food,  but  a  means  of 
carrying  food  to  the  tissues  of  all  plants  and  animals. 

Mineral  Compounds.  The  next  compounds  we  shall  take  up 
are  made  of  the  elements  mentioned  last  in  our  list:  sulphur, 
phosphorus,  iron,  potassium,  sodium,  and  calcium. 

Calcium  unites  with  sulphur  and  oxygen  to  form  calcium  sulphate, 
and  with  phosphorus  and  oxygen  to  form  calcium  phosphate. 
Sodium  and  potassium  unite  with  oxygen  and  nitrogen  to  form 
sodium  or  potassium  nitrates  and  so  on  with  many  other  com- 
pounds. 

Fortunately  we  do  not  have  to  learn  to  test  for  these  separately. 
When  found  in  organic  tissue,  they  are  usually  grouped  together 
and  called  "  mineral  matter  "  or  "  mineral  salts,"  and  the  fact 
that  they  remain  as  ash,  when  organic  matter  is  completely  burned, 
is  a  sufficient  test  for  these  compounds  at  present. 

Notice  that  all  the  elements  except  carbon  and  hydrogen  may 
exist,  combined  as  mineral  compounds,  in  the  soil  where  the  plants 
can  get  them.  Hydrogen  is  obtained  from  soil  water  and  carbon 
from  the  carbon  dioxide  of  the  air. 

All  the  compounds  mentioned  so  far,  water,  carbon  dioxide, 
and  numerous  mineral  salts,  are  inorganic  substances. 

One  of  the  most  important  ways  in  which  plants  differ  from 
animals  is  that  they  can  use  inorganic  substances  solely  for  food 


20  BIOLOGY  FOR  BEGINNERS 

and  recombine  them  into  organic  compounds,  a  thing  which  no 
animal  can  do.  Nor  can  we  imitate  it  in  any  laboratory  experiment. 

Though  animals  use  water  and  some  mineral  salts,  they  depend 
for  their  life  on  the  organic  compounds  made  by  the  plants.  Flesh- 
eating  animals  live  on  other  animals,  which  in  turn  use  plant  food. 
The  fact  that  plants  can  use  inorganic  food,  while  animals  depend 
on  plants  for  their  inorganic  nourishment,  is  one  of  the  most  im- 
portant facts  for  us  to  remember. 

Of  course  the  plant  forms  these  organic  compounds  for  its  own 
growth  and  food,  to  be  stored  away  by  the  plant  and  used  when 
necessary.  Whenever  we  eat  a  loaf  of  bread  or  a  piece  of  candy 
we  are  using  material  the  wheat  plant  or  sugar  cane  had  assimilated 
and  would  have  used  as  food  for  itself. 

ORGANIC  COMPOUNDS.    NUTRIENTS 

Fortunately,  the  very  complicated  compounds  which  the  plants 
provide  and  which  both  plants  and  animals  use  for  food  and 
growth,  can  be  grouped  into  three  great  classes  called:  (1)  Pro- 
teids,  (2)  Carbohydrates,  (3)  Fats.  These  are  sometimes  taken 
all  together  and  called  organic  nutrients. 

Proteids.  These  are  very  numerous  and  are  found  in  all  living 
substances;  the  following  are  some  that  are  common  and  found 
in  large  amounts. 

Proteid  Where  found 

Gluten  in  grains 

Legumin  in  peas  and  beans 

Myosin  in  lean  meat 

Albumen  in  the  white  of  egg 

Casein  in  milk  and  cheese 

It  is  not  necessary  to  learn  these  names  but  the  list  is  put  in 
to  show  that  proteids  are  of  many  kinds  and,  though  first  provided 
by  plants,  are  needed  in  animal  tissue  as  well. 

Test  for  Proteids.  Proteids  differ  in  many  ways  but  there  is 
one  point  in  which  they  all  behave  alike  and  which  is  different 


BIOLOGY'S  BUILDING  MATERIALS  21 

from  any  other  substance  —  hence  we  can  use  it  as  a  test.  If  a 
substance  supposed  to  contain  any  proteid  is  put  into  nitric  acid 
and  heated  gently,  it  will  turn  bright  yellow.  Then  if  the  acid  be 
washed  off  and  ammonia  added  the  proteid,  if  present,  will  become 
orange  color.  This  is  the  test  for  any  proteid  for  no  other  substance 
will  act  in  the  same  way. 

The  proteids  are  the  most  useful  of  the  nutrients  for  they  make 
up  most  of  the  active  living  substance  of  plant  and  animal;  they 
are  called  tissue  builders  on  this  account.  Proteids  are  composed 
of  the  elements  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur, 
phosphorus,  with  sometimes  mineral  salts  as  well,  so  we  see  they 
are  very  complex  organic  compounds. 

Carbohydrates.  Next  to  proteids  in  importance  to  all  living 
things  come  the  carbohydrates.  They  are  composed  of  carbon, 
hydrogen,  and  oxygen,  with  always  twice  as  much  hydrogen  as 
oxygen,  and  varying  amounts  of  carbon. 

Carbohydrates  are  found  almost  entirely  in  plants,  whose 
tissues  they  largely  compose.  When  animals  eat  them,  they 
either  make  them  over  into  proteid  tissue  or  else  oxidize  them  as 
fuel  to  produce  heat  and  energy.  Some  are  converted  into  fats 
and  stored  as  such. 

Some  common  carbohydrates  are: 

The  starches. 

Corn  starch from  corn 

Potato  starch "     potato 

Flour  starch "     wheat 

Tapioca  starch "     cassava  root 

The  sugars. 

Cane  sugar ^     SUgarCKane)  (saccharose) 

Beet  sugar sugar  beet  J 

Grape  sugar "     fruits  (Glucose) 

Milk  sugar "     milk  (Lactose) 

Cellulose. 

Complicated  forms  found  in  wood,  paper,  cotton,  linen. 


22  BIOLOGY  FOR  BEGINNERS 

(Glycogen  is  an  animal  carbohydrate  found  in  the  liver  of  some 
animals  and  called  "  liver  starch."  It  seems  to  be  stored  there  for 
later  use.) 

It  is  a  little  strange  to  think  of  cotton  and  starch,  or  wood  and 
sugar  as  being  so  nearly  related,  but  they  consist  of  the  same  three 
elements,  and  are  produced  by  the  plants  from  water  and  carbon 
dioxide.  It  would  be  a  cheap  diet,  if  we  could  take  water  from 
a  reservoir  and  carbon  dioxide  from  the  air  and  make  them  into 
flour.  'Man  has  to  depend  on  plants  for  this  wonderful  process, 
and  can  only  begin  where  the  plants  leave  off,  using  the  plant- 
made  carbohydrates  for  his  food. 

The  Test  for  Starches.  No  one  test  can  be  used  for  all  the  carbo- 
hydrates, but  we  can  test  for  any  starch  by  dissolving  the  substance 
supposed  to  contain  it  in  hot  water  and  then  adding  a  drop  of 
iodine.  The  solution  will  turn  blue  if  starch  be  present.  No 
substance  other  than  starch  will  act  this  way  under  these 
conditions. 

The  Test  for  Grape  Sugar.  There  is  no  one  test  for  all  sugars, 
but  grape  sugar  (glucose)  is  very  common  and  can  be  easily  dis- 
tinguished from  our  household  (beet  or  cane)  sugar  by  what  is 
known  as  the  Fehling  Test  —  so  named  from  the  man  who  devised  it. 

Two  solutions  are  used  in  the  Fehling  test,  one  colorless,  and  one 
blue.  When  these  are  added  in  equal  amounts  to  a  similar  amount 
of  the  substance  to  be  tested,  and  the  mixture  heated,  a  yellow- 
brown  solid  will  form  if  grape  sugar  be  present.  Cane  or  beet  sugar 
will  not  act  this  way. 

Fats.  The  last  class  of  nutrients  is  the  fats  and  oils,  which  are 
also  composed  of  carbon,  hydrogen,  and  oxygen.  They  differ 
from  carbohydrates  in  having  less  oxygen.  Hence  they  oxidize 
more  readily  and  as  a  result  their  chief  use  is  to  produce  energy. 

Plants  store  fats  in  their  seeds  to  supply  energy  for  growth; 
animals  store  fats  in  various  places  and  use  them  for  the  same 
purpose. 

Kinds.  Cotton-seed  oil,  olive  oil,  and  the  oils  from  various 
nuts  are  examples  of  vegetable  fats;  while  lard,  butter,  and  fat 
meats  are  familiar  examples  of  fat  from  animals. 


BIOLOGY'S   BUILDING   MATERIALS 


23 


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24  BIOLOGY  FOR  BEGINNERS 

Test  for  Fats.  To  test  for  fats  the  substance  should  be  crushed 
as  finely  as  possible  and  treated  with  ether.  This  will  dissolve 
out  any  fat  that  may  be  present  and  can  then  be  poured  off.  When 
the  ether  evaporates  the  fat  will  remain  in  the  dish. 

COLLATERAL   READING 

See  index  of  any  Chemistry  Text  for  the  Compounds  mentioned.  General 
Biology,  Sedgwick  and  Wilson,  pp.  33-40;  Biology,  Bailey  and  Coleman, 
Introduction;  Elementary  Biology,  Peabody  and  Hunt,  pp.  13-25;  Chemis- 
try of  Plant  and  Animal  Life,  Snyder,  see  index;  Source,  Chemistry  and 
Use  of  Food  Products,  Bailey,  pp.  1-24;  Food  Products,  Sherman,  pp.  1-23; 
Botany  for  Schools,  Atkinson,  pp.  13-19. 


CHAPTER  V 

PROTOPLASM,  THE   "BIOS"   OF  BIOLOGY 

Vocabulary 
Protoplasm,  see  text. 

Fundamental,  that  upon  which  all  else  is  built. 
•     Essential,  necessary. 

Nucleus,  most  active  part  of  cell  protoplasm,  controls  growth 

and  reproduction  —  usually  visible  as  a  denser  spot. 
Minute,  very  small. 

Function,  use  or  work  of  a  special  part. 
Adaptation,  fitness  for  use. 
Environment,  all  that  makes  up  the  surroundings  of  any  living 

thing. 
Primary,  first  in  origin  and  importance. 

Since  it  appears  that  plants  and  animals  are  composed  of  the 
same  elements  and  use  similar  compounds  for  food  it  would  be 
only  natural  that  their  foundation  material  should  be  the  same. 
This  is,  in  fact,  the  case.  The  foundation  substance  is  called 
protoplasm,  a  name  derived  from  two  Greek  words,  protos  (first) 
and  plasma  (form  or  substance).  It  is  well  named,  for  it  is  the 
first  and  most  necessary  substance  of  all  organic  things. 

Protoplasm  is  alive  and,  in  truth,  the  only  living  substance.  We 
do  not  know  what  life  is  but  we  do  know  that  as  long  as  life  exists 
in  plants  or  animals,  their  protoplasm  is  active.  When  it  ceases 
to  act,  death  is  the  result. 

Protoplasm  may  be  defined  as  the  fundamental,  essential,  living 
substance  of  all  plants  and  animals.  It  is  a  jelly-like  substance 
composed  of  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  and 
phosphorus;  but  while  we  can  analyze  it  and  state  its  composi- 
tion, we  cannot  combine  the  elements  to  make  it.  There  is  only 
one  Power  that  can  create  life. 

25 


.26  BIOLOGY  FOR  BEGINNERS 

Because  it  is  alive,  protoplasm  has  certain  remarkable  properties: 

1.  It  takes  in,  digests,  and  assimilates  food. 

2.  It  oxidizes  food  and  excretes  waste. 

3.  It  grows  in  size  and  form. 

4.  It  has  power  of  motion. 

5.  It  responds  to  light,  heat,  moisture,  etc. 

6.  It  reproduces. 

D/ A  SIT Atf    OF    4    TYPICAL    C£IL 


FIG.  3.     Animal  and  plant  cells  similar  in  structure  but  varying  in  form. 


We  observe  that  this  list  is  much  like  the  one  which  gave  the 
points  in  which  the  cat  resembled  the  geranium.  Now  we  can  see 
the  reason:  both  depend  on  protoplasm  for  life,  so,  of  course,  their 
life  processes  would  be  similar. 


PROTOPLASM  27 

The  Cell.  In  most  plants  and  animals  the  protoplasm  is  divided 
into  very  small  parts  called  cells.  These  are  merely  the  simplest 
units  of  protoplasm  of  which*  the  plant  or  animal  is  composed. 
A  living  cell  usually  consists  of  a  tiny  mass  of  protoplasm  surrounded 
by  a  membrane  called  the  cell  wall.  The  central  portion  of  the 
protoplasm,  more  active  than  the  rest,  is  called  the  nucleus.  The 
cell  wall  gives  definite  shape  to  the  cell  and  the  nucleus  seems  to 
regulate  growth  and  reproduction.  Cells  are  usually  very  minute, 
but  are  of  innumerable  shapes,  varying  with  the  special  work  they 
may  have  to  perform. 

Some  plants  and  animals  consist  of  only  one  cell.  In  more 
complicated  animals,  there  are  a  great  many  different  groups  of 
cells,  each  fitted  for  some  one  purpose,  as,  for  example,  the  vast 
number  of  cells  that  together  make  up  a  muscle  and  have  developed 
especially  the  power  of  motion. 

Tissues.  A  group  of  similar  cells,  devoted  to  a  single  use,  is 
called  a  tissue.  There  are  many  kinds  of  tissues,  as  wood,  bark, 
and  leaf,  in  plants,  and  bone,  muscle,  nerve,  etc.,  in  animals. 

Organs.  In  all  the  more  familiar  plants  and  animals,  various 
tissues  are  grouped  together  to  form  a  more  complex  part,  which 
has  some  important  general  use.  The  stem  of  a  tree,  for  instance, 
whose  use  is  to  support  the  leaves,  flowers,  and  fruit,  consists  of 
wood,  pith,  bark,  and  other  tissues,  all  working  together  for  one 
purpose.  The  leg  of  a  cat  is  made  up  of  bone,  muscle,  nerve,  and 
other  tissues,  working  together  to  make  locomotion  possible.  Such 
groups  of  tissues  are  called  organs  and  the  purpose  or  use  of  any 
part  is  called  its  function. 

So  we  can  say  that  all  living  things  are  composed  of  protoplasm; 
the  protoplasm  is  usually  divided  into  cells;  the  cells  are  grouped 
into  tissues,  and  these,  in  turn,  into  organs  fitted  for  some  particular 
function  or  functions. 

Systems.  Often  in  the  higher  forms,  especially  among  animals, 
several  organs  are  grouped  together  to  perform  related  functions. 
Such  groups  are  referred  to  as  systems,  as,  for  example,  the  circu- 
latory system,  which  includes  the  heart,  arteries,  veins,  and  capil- 
laries. These  are  organs,  all  united  in  the  work  of  circulation. 


28  BIOLOGY  FOR  BEGINNERS 

The  comparison  is  sometimes  made  between  a  plant  or  animal 
and  a  book,  as  follows: 

The  elements  correspond   to  the  letters. 

Compounds  correspond    to  words. 

Cells  correspond    to  sentences. 

Tissues  correspond    to  paragraphs. 

Organs  correspond    to  chapters. 

The  plant  or  animal  corresponds  to  the  whole  book. 

To  illustrate  this  method  of  structure  we  may  look  at  the  hand. 
It  is  made  of  millions  of  cells,  as  shown  by  the  microscope,  each 
having  its  characteristic  shape  and  the  usual  cell  parts:  protoplasm, 
nucleus,  and  wall. 

Numerous  as  these  cells  are,  they  can  be  classified  into  a  com- 
paratively few  kinds.  Groups  of  similar  cells  are  called  tissues, 
and  we  find  in  the  hand,  muscle  tissue,  bone  tissue,  nerve  tissue, 
skin  tissue,  and  some  others.  Each  of  these  tissues  has  its  special 
use.  The  muscle  is  used  for  motion;  the  bone,  for  support;  and 
so  on.  All  together  they  are  combined  into  one  organ',  whose 
general  function  is  prehension  (grasping  things). 

In  a  similar  way  with  plants,  the  cell  is  the  unit  of  structure, 
and  in  a  stem,  for  instance,  there  are  several  kinds  of  cells.  These 
are  grouped  into  wood  tissue,  bark  tissue,  tubular  tissue,  and  pith 
tissue,  each  made  of  similar  cells  and  each  with  different  functions. 
However,  they  are  all  grouped  together  to  form  the  plant  organ, 
called  the  stem,  with  its  general  functions  of  support  and  circulation 
of  sap. 

Relation  of  Structure  to  Use.  Organic  things  are  composed  of 
the  same  elements,  combined  in  similar  compounds,  which  appear 
as  living  protoplasm,  whether  of  animals  or  plants.  This  proto- 
plasm performs  very  similar  functions  in  either  case,  but  by  very 
different  organs.  The  plant  gets  its  food  by  way  of  leaves  and 
roots,  while  an  animal  like  the  cat  uses  its  claws,  teeth,  and  swift- 
ness. Our  whole  course  in  biology  deals  with  the  essential  life 
functions  of  plants  and  animals,  but,  in  order  to  study  these  func- 


PROTOPLASM  29 

tions  intelligently,  we  must  first  know  something  of  the  structure 
of  the  organs  concerned  in  their  performance. 

As  soon  as  one  understands  structure  in  its  relation  to  function 
it  becomes  apparent  that  each  organ  is  wonderfully  fitted  for  its 
particular  work.  This  fitness  of  structure  to  function  is  called 
adaptation,  and  is  a  very  important  topic  in  all  biologic  study. 
Structure,  function,  and  adaptation  are  the  foundation  stones  of 
our  subject  and  will  always  be  presented  hi  the  order  here  named. 
We  shall  study  both  plants  and  animals  with 'the  idea  of  learning 
how  their  structure  adapts  them  for  the  functions  which  both 
have  in  common  and  shall  begin  with  plants,  because,  while  their 
functions  are  similar  to  those  characteristic  of  animals,  their 
structure  is  much  simpler.  The  following  functions  are  common 
to  both  plants  and  animals: 

Food  getting  Excretion 

Digestion  Motion 

Absorption  Sensation 

Assimilation  Reproduction 
Respiration 

We  know  already  the  names  of  the  principal  organs  of  a  plant  — 
the  root,  stem,  leaves,  flower,  fruit,  and  seed  —  and  understand,  in 
some  measure  the  functions  performed  by  each.  We  must  also 
remember  the  varied  surroundings  of  the  plant,  the  kind  of  soil, 
amount  of  moisture,  temperature,  insect  enemies,  and  all  that  goes 
to  make  up  its  conditions  of  life  (environment).  In  our  study  we 
shall  start,  as  the  plant  starts,  with  the  seed.  Then  we  will  follow 
an  account  of  its  growth,  and  the  development,  structure,  and 
use  of  the  different  plant  parts  mentioned  above. 

COLLATERAL  READING 

General  Biology,  Sedgwick  and  Wilson,  pp.  20-32;  Applied  Biology, 
Bigelow,  pp.  39-44;  Elementary  Biology,  Peabody  and  Hunt,  pp.  29-32; 
Essentials  of  Biology,  Hunter,  pp.  31-33;  Botany  for  Schools,  Atkinson, 
pp.  33-36;  Botany  of  Crop  Plants,  Robbins,  pp.  4-9;  Fundamentals  of 
Botany,  Gager,  pp.  14-20;  Plant  Anatomy,  Stevens,  1-10;  Plant  Physi- 


30  BIOLOGY  FOR  BEGINNERS 

ology,  Duggar,  pp.  15-32;  College  Botany,  Atkinson,  pp.  1-12;  Biology, 
Calkins,  pp.  6-25;  Encyclopedia  Britannica,  articles  on  "Physiology," 
"Protoplasm,"  "Protozoa." 

SUMMARY 

Protoplasm  is  the  primary,  essential  living  substance  of  all  plants  and 

animals. 
A  cell  is  the  simplest  unit  of  plant  or  animal  structure.     It  consists  of 

protoplasm,  nucleus,  and  cell  wall. 

A  tissue  is  a  group  of  similar  cells  having  a  special  function. 
An  organ  is  a  group  of  various  tissues,  having  a  general  function. 
A  system  is  a  group  of  organs  concerned  in  one  or  more  related  functions. 

1.  Protoplasm. 

Derivation:  Protos,  Plasma. 

Definition. 

Composition:  C,  H,  O,  N,  S,  P. 

Properties : 

(1)  Takes  and  assimilates  food. 

(2)  Oxidizes  and  excretes  waste. 

(3)  Growth. 

(4)  Motion. 

(5)  Response  to  heat,  light,  etc. 

(6)  Reproduction. 

2.  The  cell. 

Definition. 

Essential  parts  Function 

Protoplasm.  Any  of  above  properties. 

Cell  wall.  Gives  form  to  cell. 

Nucleus.  Controls  growth  and  reproduction. 

(Diagram) 

3.  Tissue. 

Definition. 
Examples. 

4.  Organ. 

Definition. 
Examples. 

5.  System. 

Definition. 
Examples. 

6.  Relation  of  Structure  to  Use.. 

Similarity  of  functions. 

Difference  of  structures. 

Adaptation  or  fitness  of  structure  to  function. 

7.  Order  for  study. 

Structure,  function,  adaptation, 


CHAPTER  VI 
THE  STRUCTURE  OF  SEEDS 

Vocabulary 

Immature,  not  fully  developed. 
Primitive,  simple  or  early  form  of  an  organ. 
Transmit,  carry  (similar  to  transport). 
Modified,  changed  for  different  use. 

It  is  so  common  a  fact  that  a  seed  reproduces  the  whole  plant 
that  the  wonder  of  it  is  often  overlooked.  In  the  seed  must  exist, 
alive,  all  the  beginnings  for  the  full-grown  plant,  together  with 
nourishment  to  start  growth  and  adequate  protection. 

The  seed,  then,  is  a  plant  organ  which  consists  of  three  parts: 
the  immature  plant  (embryo),  stored  food,  and  protective  coverings. 

Seed  Coats.  The  outer  covering  of  most  seeds  is  called  the 
testa,  and  is  usually  thick  enough  to  protect  from  injury  by  contact, 
moisture,  or  insects.  It  may  also  have  special  adaptations  for 
dispersal.  A  second  inner  thin  coat  (tegumen)  is  present  in  some 
seeds. 

Since  the  seed  was  once  a  part  of  the  parent  plant,  it  bears  a 
scar  on  the  testa,  called  the  hilunt,  which  marks  this  point  of 
previous  attachment.  Near  this  scar  is  usually  visible  a  tiny 
opening  called  the  micropyle,  from  two  Greek  words  meaning 
"  little  door."  This  little  door  has  two  uses;  it  lets  the  pollen 
enter  the  seed  when  it  is  fertilized  (see  Chapter  XIV),  and  it  lets 
the  young  plant  out  when  it  begins  its  growth. 

Kernel.  Within  these  coats  is  the  kernel  or,  seed  proper.  It 
may  consist  wholly  of  the  undeveloped  plant  (embryo);  or  may 
have,  outside  the  embryo,  a  store  of  nourishment  called  the 
endosperm. 

31 


32 


BIOLOGY  FOR  BEGINNERS 


—  TYPICAL  SEED  — 

rut     INTtHHKL       iTRUCTUXC 


Embryo.  If  endosperm  be  present,  the  embryo  may  be  poorly 
developed,  even  showing  no  sign  of  its  usual  parts,  as  in  the 
orchids.  On  the  other  hand,  the  embryo  may  be  highly  developed 
and  show  well-defined  stem  and  leaves,  as  in  the  bean;  for  since 
there  is  no  endosperm  in  the  bean,  the  plantlet  must  seek  its  own 
nourishment  very  early.  The  embryo,  or  miniature  plant,  consists 
of  three  parts:  the  cotyledons,  plumule,  and  hypocotyl. 

Cotyledons.  These  are  the  seed  leaves  or  the  first  leaves  of  the 
plant  and,  though  often  not  resembling  ordinary  leaves  either  in 

appearance  or  use,  still 
play  a  very  important 
part  in  the  early  growth 
of  the  seedling.  They 
may  be  really  leaf-like 
and  come  up  when  the 
plant  begins  to  grow, 
forming  true  green  leaves, 
as  in  the  squash.  In  this 
case  they  are  thin  and 
have  little  stored  food, 
because  they  get  all  they 
need  as  soon  as  they  rise 
above  the  soil.  On  the 
other  hand  the  cotyle- 
dons may  be  so  well  sup- 
plied with  food  that  they  cannot  act  as  leaves  at  all,  merely  coming 
above  ground,  giving  over  their  stored  food  to  the  growing  seedling, 
and  then  withering  and  dropping  off,  as  is  the  case  with  most  beans. 
In  other  cases,  such  as  the  pea,  the  cotyledons  are  so  greatly  en- 
larged .with  food,  that  they  cannot  be  lifted  from  the  soil  at  all, 
and  so  supply  the  plant  from  their  place  in  the  ground  below. 
In  cases  where  the  food  is  stored  outside  the  embryo  as  the  endo- 
sperm, the  cotyledon  often  remains  in  contact  with  it  to  digest  and 
transfer  food  from  endosperm  to  embryo,  as  is  the  case  in  corn. 
Not  only  do  the  cotyledons  vary  in  size  and  use  (function), 
but  also  in  number,  there  being  only  one  in  many  plants  such 


FIG.  4.    The  internal  structure  of 
a  typical  seed. 


THE  STRUCTURE  OF  SEEDS  33 

as  corn  and  other  grasses,  lilies,  palms,  etc.,  two  in  many  common 
plants  like  the  bean,  squash,  apple,  and  buttercup,  and  many  in 
pines  and  other  evergreens.  So  important  is  this  difference  that 
all  plants  that  bear  seeds  are  classified  as: 

Monocotyledonous  (having  one  cotyledon), 
Dicotyledonous  (having  two  cotyledons), 
Polycotyledonous  (having  three  or  more  cotyledons), 

and  can  be  placed  in  one  of  these  three  divisions,  which  also  agree, 
as  well,  in  structure  of  stem,  leaf,  and  flower. 

Plumule.  The  plumule  is  that  part  of  the  embryo  above  the 
cotyledons,  from  which  develops  the  shoot  proper,  consisting  of 
stem,  leaves,  and  flowers.  It  may  vary  much  in  size  and  develop- 
ment. If  much  food  be  stored,  either  in  cotyledons  or  endosperm, 
the  plumule  may  be  small.  On  the  other  hand  if  little  food  be 
provided,  the  plant  must  early  shift  for  itself,  and  so  the  plumule 
may  have  several  well-formed  leaves,  wanting  only  exposure  to 
light  to  become  a  self  supporting  plant. 

Hypocotyl.  The  primitive  stem,  or  all  that  part  of  the  embryo 
below  the  cotyledons,  is  the  hypocotyl.  From  its  lower  end  the 
root  system  develops.  Upon  its  upward  lengthening  depends 
whether  the  cotyledons  shall  emerge  from  the  soil  when  germination 
takes  place. 

Endosperm.  Though  the  endosperm  is  usually  present  at  some 
stage,  it  is  not  found  in  all  seeds  when  they  are  mature,  since  it 
may  be  entirely  absorbed  by  the  growing  embryo,  its  function  of 
food  storage  being  assumed  by  the  cotyledons.  It  is,  however, 
very  important  in  many  seeds,  especially  the  grains.  From  its 
store  of  starch  we  derive  our  bread.  Food  for  the  embryo  may 
be  stored  either  in  the  endosperm  or  cotyledons.  Our  laboratory 
tests  show  that  this  stored  food  consists  largely  of  starch,  to- 
gether with  considerable  proteid,  a  little  fat  or  oil,  and  some 
mineral  matter. 

The  seed  has  within  itself  the  miniature  plant',  or  embryo,  and 
all  the  kinds  of  nutrients  needed  for  growth  except  water.  This 


34  BIOLOGY  FOR  BEGINNERS 

the  seed  must  get  from  the  soil  before  it  can  grow.  The  growth  of 
a  seed  is  a  very  wonderful  process.  Though  inactive,  dry,  and 
apparently  dead  the  protoplasm  is  really  alive  and  only  awaits 
favorable  conditions  for  growth  to  begin. 

The  insoluble,  stored  foods  must  be  digested  by  the  embryo, 
made  soluble,  united  with  the  water  which  has  been  absorbed  from 
the  soil,  and  assimilated,  to  form  all  the  new  kinds  of  tissue  in 
the  growing  seedling.  It  may  seem  strange  to  speak  of  a  seed  as 
digesting  food,  but  there  is  a  substance  (diastase)  in  the  seed, 
which  digests  its  food  just  as  truly  as  the  fluids  of  our  stomach 
digest  ours.  Here,  then,  are  digestion,  absorption,  and  assimila- 
tion going  on  in  the  seed  as  it  begins  to  grow.  If  the  food  stuffs 
in  the  seed  were  not  stored  in  a  dry  and  insoluble  form,  they 
would  dissolve  and  decay.  It  is  necessary,  therefore,  if  a  seed 
is  to  keep  over  winter,  that  its  food  must  be  both  dry  and 
insoluble. 


EXAMPLES  OF  SEED  STRUCTURE 

Each  seed  differs  somewhat  from  the  general  description  just 
given;  the  parts  of  the  embryo  may  be  well  or  poorly  developed; 
the  number  of  cotyledons  may  vary;  and  the  endosperm  may  be 
lacking  altogether. 

All  that  is  necessary  for  a  true  seed  is  the  embryo,  stored  food, 
and  protective  coverings.  These  are  often  very  different  in 
structure,  to  adapt  them  to  various  surroundings. 

The  bean  is  presented  as  an  example  of  a  dicotyledonous  seed 
without  endosperm,  while  the  corn  is  taken  as  a  type  of  a  mono- 
cotyledonous  seed  in  which  there  is  a  very  large  endosperm. 

The  Bean.  .External  Structure.  This  familiar  seed  is  usually 
kidney-shaped  or  oval  in  outline,  several  being  borne  in  a  pod, 
which  is  the  true  fruit  of  the  plant. 

The  testa  is  usually  smooth  and  may  be  variously  colored;  on 
the  concave  side  it  bears  a  scar  (hilumj,  marking  where  it  was 
attached  to  the  pod.  By  means  of  this  attachment  it  also  received 
nourishment  when  growing  on  the  parent  plant. 


THE   STRUCTURE  OF  SEEDS 


35 


Near  the  hilum  is  a  tiny  opening  (micropyle),  and  toward  this 
there  sometimes  extends  a  ridge  which  shows  the  location  of  the 
hypocotyl,  which  will  emerge  here  on  germination. 

The  tegumen  is  very  thin  and  often  cannot  be  separated  from 
the  testa. 

The  Bean.  Internal  Structure.  On  removing  the  seed  coats, 
the  kernel  is  seen  to  consist  of  the  embryo  only,  the  endosperm 
having  been  completely  ab- 
sorbed. All  the  nourishment 
is  now  stored  in  the  cotyle- 
dons which  are  large,  not  at 
all  leaf-like,  and  contain 
much  proteid  and  starch. 

The  hypocotyl  is  seen  as  a . 
linger-like  projection,  fitting 
into  a  protective  pocket  in 
the  seed  coats.  To  it  the 
cotyledons  are  attached  on 
either  side. 

By  removing  one  "  half  " 
(cotyledon)  of  the  bean,  the 
plumule  is  exposed,  attached 
to  the  hypocotyl  above  the 
cotyledons  and  closely  pack- 
ed in  between  their  ends.  It 
is  fairly  well  developed  and 
can  be  seen  to  consist  of  two 
small  leaves,  with  well-mark-  ( 

FIG.  5.     Structure    of    bean,    exterior; 


ed  veins,  folded   over   each 


with  seed  coats  removed ;  with  one  cotyl- 
edon removed. 


Other. 

It  will  be  noted  that  the 
upper  end  of  the  hypocotyl  is  the  one  point  where  all  three  parts 
of  the  embryo  are  united.  When  the  cotyledon  is  removed,  a  scar 
showing  its  place  of  attachment  is  left  on  the  side  of  the  hypocotyl. 

The  pea  seed  shows  a  structure   similar  to  that  of  the  bean 
except  that  the  cotyledons  are  so  enormously  swelled  with  stored 


36 


BIOLOGY  FOR  BEGINNERS 


FIELD    CORN       KtRNEL 


food  that  they  do  not  come  above  ground  as  do  most  beans.    They 
remain  below  and  never  approach  the  appearance  of  leaves. 

However,  having  so  much  stored  food,  the  plumule  of  the  pea 
does  not  need  to  develop  early,  so  is  very  small,  and  even  when 
growth  commences,  the  first  leaves  of  the  plumule  are  mere  scales, 
and  do  not  have  much  ability  to  get  food.  The  true  leaves  do  not 

make  their  appearance  till  the  food  in 
the  cotyledons  becomes  scant. 

Corn.  External  Structure.  The  corn 
seed,  as  it  is  usually  called,  is  really  a 
fruit  corresponding  to  the  bean  pod, 
rather  than  to  the  bean  itself.  One  seed 
completely  fills  the  fruit,  so  that  the 
seed  coats  and  fruit  coats  cannot  be 
distinguished. 

As  a  result  of  this  fact,  the   hilum 
and  micropyle  are  covered  by  the  fruit 
coats  and  what  might  be  mistaken  for 
the  hilum  is  really  the  point  of  attach- 
ment of  the  corn  fruit  (grain)  to  the  cob. 
On  one  side  of  each  grain  can  be  seen  a 
light-colored,  oval  area,  which  marks  the 
location  of  the  embryo,  visible  beneath 
the  coats.    On  the  same  side,  but  at  the 
FIG.  6.    External  and  in-   end  opposite  the  point  of  attachment,  is 
ternal  structure  of  corn  seed,   located    a    tiny    point,    the    silk    scar, 

where  the  corn  "  silk  "  formerly  grew. 

Corn.  Internal  Structure.  Internally  the  corn  consists  of  a 
large  endosperm,  containing  much  starch,  proteid,  and  some  oil, 
and  at  one  side  near  the  point  of  the  grain,  a  much  smaller  part, 
the  embryo. 

This  embryo  has  but  one  cotyledon,  a  rather  irregular,  oval 
structure,  wrapped  around  the  plumule  and  hypocotyl,  and  lying 
in  close  contact  with  the  endosperm.  Its  function  is  to  digest  and 
transmit  the  food  stored  in  the  endosperm  to  the  growing  seedling. 
It  is  a  real  digestive  organ,  which  secretes,  ferments,  and  makes 


•Slllt  S(AH 


fr  orATTftHnnnr, 


THE   STRUCTURE  OF  SEEDS 


37 


the  food  soluble,  just  as  truly  as  does  an  animal's  stomach  or 
intestine. 

The  hypocotyl  of  the  corn  is  a  small  pointed  organ,  aimed  toward 
the  attached  end  of  the  grain,  thus  leading  us  to  suppose  the 
micro pyle  to  be  in  that  region.     It  is  covered  with  a  cap  which  pro 
tects  it  as  it  passes  through  the  soil  when  the  root  begins  to  develop. 


STRUCTURE      or    CORN      EAR 

FIG  .  7.    The  corn  ear  is  really  a  spike  of  fruits  closely  grown  together. 

The  plumule  is  also  protected  by  a  sheath  or  cap,  and  consists 
of  several  very  small  leaves  rolled,  not  folded,  into  a  compact 
"  spear  "  which  can  safely  push  upward  through  the  earth. 

The  cob,  on  which  the  kernels  are  borne,  is  really  a  stem  of  the 
spike  of  flowers,  each  of  which  produces  one  kernel.  Thus  the  corn 
ear  will  be  seen  to  be  a  spike  of  fruits,  closely  grown  together, 


38  BIOLOGY  FOR  BEGINNERS 

and  not  a  single  fruit  like  a  bean  pod.  The  chaff  around  the  grains 
represents  some  of  the  outer  flower  parts  while  the  silk  is  a  portion 
of  the  central  organ  of  the  flower  called  the  pistil,  and  its  function 
is  to  catch  and  transmit  the  pollen  grains.  This  will  be  explained 
in  the  chapter  on  fertilization.  The  husks  are  modified  leaves 
developed  to  protect  the  corn  ear. 

Bean  Corn 

Has  hilum,  testa,  micropyle  Hilum,  etc.,  covered  by  fruit 

coats 

Two  cotyledons  One  cotyledon 

Large  embryo  Small  embryo 

No  endosperm  Large  endosperm 

Plumule  fairly  large  Plumule  rather  small 

Plumule  leaves  folded  Plumule  leaves  rolled 

The  fruit  a  pod,  with  many  The  fruit  a  single  grain,  with 

seeds         •  one  seed 

COLLATERAL   READING 

Lessons  in  Botany,  Atkinson,  pp.  2-208;  Natural  History  of  Plants, 
K.  and  O.,  Vol.  I,  p.  601;  Natural  History  of  Plants,  Vol.  II,  p.  450; 
Lessons  with  Plants,  Bailey,  pp.  132-133,  252;  Plant  Structures,  Coulter, 
pp.  183-184,  210-214;  Studies  on  Plant  Life,  Atkinson,  pp.  158-192; 
Practical  Botany,  S.  and  H.,  p.  343;  Plant  Relations,  Coulter,  pp.  111-115, 
138-140;  Seed  Babies  (L),  Moreley,  entire;  Elementary  Studies  in  Botany, 
Coulter,  pp.  317-325;  Plant  Life  and  Uses,  Coulter,  pp.  325-353;  Experi- 
ments in  Plants,  Osterhout,  pp.  1-68;  Practical  Biology,  Small  wood, 
pp.  259-267;  Cornell  Leaflets,  Bui.  L,  pp.  401-414. 

SEED   STRUCTURE 
Definition  of  seed. 

A  plant  orsjan  whose  function  is  to  reproduce  the  plant,  consisting  of: 

1.  The  living  miniature  plant  (embryo). 

2.  Stored  food. 

3.  Protective  coverings. 
Structure  of  seeds. 

1.    Coats.     Function,  Protection. 
Testa  (outer  coat). 

Hilum  (scar  on  testa).    Point  of  attachment  for  supply  of 

nourishment. 

Micropyle  (opening).    Entrance  of  pollen,  exit  of  hypocotyl. 
Tegumen  (inner  coat). 


THE   STRUCTURE  OF  SEEDS  39 

2.    Kernel. 

Embryo  (miniature  plant,  always  present). 

(1)  Cotyledons  (seed  leaves) 
Development. 

(a)  Leaf-like  (squash). 

(b)  Store  food,  but  come  up  (bean). 

(c)  Store  food  below  ground  (pea). 

(d)  Digest  and  absorb  from  endosperm  (corn). 
Number. 

(a)  Monocotyledonous  (one  cotyledon)  (corn). 

(b)  Dicotyledonous  (two  cotyledons)  (bean). 

(c)  Polycotyledonous  (several)  (pine). 

(2)  Plumule  (undeveloped  shoot). 
Development. 

(a)  Small  if  much  stored  food. 

(b)  Large  if  little  stored  food. 

(3)  Hypocotyl  (part  below  cotyledons). 
Development. 

(a)  Root  from  lower  end. 

(b)  Raises  cotyledons  if  it  grows  up. 
Endosperm  (stored  food,  may  be  lacking). 

(a)   Why  not  always  present? 

(&)   Use  to  man. 
Food  in  seeds. 

May  be  stored  in  cotyledons  or  endosperm. 
Why  stored  dry  and  nearly  insoluble. 
Need  of  digestion,  use  of  diastase. 

TYPES    OF    SEED    STRUCTURE 

Bean  (Dicot.,  no  endosperm).     The  pod  is  the  fruit. 
External  structure. 
Shape,  colof,  etc. 
Testa. 

Hilum,  caused  by  attachment  to  pod,  used  to  receive  nourishment 

from  plant. 

Micropyle,  used  for  exit  of  hypocotyl  (see  ridge), 
used  for  ingress  of  pollen  (see  fertilization). 
Tegumen,  thin,  unimportant. 
Internal  structure. 
Kernel. 

No  endosperm  (what  has  become  of  it?). 
Cotyledons,  two,  large  and  rather  thick. 

contain  starch  and  proteid. 

Hypocotyl,  finger  shaped.    In  protective  pocket. 
Plumule,  moderately  developed,  two  plain  leaves,  veins,  etc. 


40  BIOLOGY  FOR  BEGINNERS 

Corn  ("Kernel"  is  the  true  fruit). 
External  structure. 

Seed  coats  covered  by  fruit  coats. 
Hilum  and  micropyle  hidden. 
Items  to  be  located. 

Point  of  attachment  to  cob,  at  narrow  end. 
Embryo  mark  on  side. 
Silk  scar  at  broad  end. 
Internal  structure. 

Endosperm,  large  —  much  stored  starch,  proteid,  oil. 
Embryo. 

Cotyledon,  one,  oval,  against  the  endosperm,  used  to  digest  and 

transmit  food,  has  ferments  for  digestion. 
Hypocotyl,  protective  cap,  points  to  attached  end  of  seed. 
Plumule,  protective  cap,  rolled  leaves,  adapted  for  piercing  soil. 
Cob,  the  stem  of  flower  spike. 
Chaff,  outer  flower  parts. 
Kernel,  the  fruit. 

Silk,  the  pistil  for  catching  pollen. 
Husks,  leaves  for  protection. 


CHAPTER  VII 

GERMINATION  — THE   SEED   WAKES  UP 

Vocabulary 

Distinct,  of  separate  kinds. 
Tolerate,  to  bear  or  endure. 
External,  pertaining  to  the  outside. 
Dispersal,  the  act  of  scattering,  as  pf  seeds. 
Emergence,  coming  out  of  anything. 
Penetration,  forcing  a  way  through 

The  seed  is  not  a  thing  totally  distinct  from  the  parent  plant, 
though  it  is  separated  from  it.  It  contains  the  same  protoplasm 
as  the  parent  plant,  with  this  distinction;  its  protoplasm  is  in  a 
condition  of  rest.  The  seed  is  not  dead,  it  is  asleep  and  waits 
only  for  favorable  conditions  to  wake  into  the  activity  of  growth. 

Function  of  the  Seed.  This  resting  stage  is  of  two-fold  value  — 
it  condenses  the  essential  nature  of  the  whole  plant  within  small 
compass,  capable  of  easy  and  wide  dispersal,  and,  most  important 
of  all,  protects  the  vitality  of  the  embryo  so  that  the  seed  can 
withstand  periods  of  drought,  cold,  heat,  or  other  conditions 
which  would  be  fatal  to  the  parent  plant. 

Both  dispersal  and  preservation  are  steps  toward  the  chief 
function  of  the  seed,  which  is  to  reproduce  the  plant  that  is  at 
rest  within  it.  This  resumption  of  active  life  is  called  germination. 

Necessary  Conditions  for  Germination.  For  the  germination  of 
most  seeds  at  least  three  conditions  are  required,  in  amounts 
varying  between  wide  but  definite  limits;  these  are  moisture, 
heat,  and  air. 

There  are  a  few  plants  whose  seed  will  develop  under  water 
while  others  retain  enough  of  the  scant  dews  of  the  desert  nights 
to  waken  the  seed  into  growth.  Usually,  however,  a  moderate 

41 


42  BIOLOGY  FOR  BEGINNERS 

water  supply  is  essential,  too  much  causing  decay,  and  too  little 
precluding  growth  altogether. 

As  to  temperature,  a  maple  seedling  will  germinate  on  a  cake 
of  ice  and  many  other  seeds  grow  in  extreme  cold,  while  a  smaller 
number  tolerate  high  temperatures.  The  majority,  however, 
germinate  most  freely  between  60°  and  80°  F. 

Air  from  some  source  is  essential  to  growth,  for  seeds,  like  all  living 
things,  must  breathe.  Many  can  obtain  the  needed  supply  even 
from  the  air  dissolved  in  the  water  in  which  they  maybe  submerged. 

In  addition  to  these  external  conditions,  the  embryo  must  also 
have  a  supply  of  stored  food  for  immediate  use  while  the  roots 
and  leaves  are  developing.  This  food  may  be  stored  in  the  coty- 
ledons, as  in  the  bean  and  pea,  or  outside  the  embryo,  as  in  the 
case  of  the  endosperm  of  the  corn  and  other  grains. 

Stages  in  Germination.  Germination  consists  of  three  steps, 
emergence  from  the  seed  coats,  penetration  of  the  soil,  and  the 
obtaining  of  first  nourishment. 

In  getting  out  of  the  seed  coats,  the  hypocotyl  appears  first, 
emerging  by  way  of  the  micropyle.  The  rest  of  the  embryo  follows 
by  various  ingenious  schemes,  all  apparently  planned  by  Nature 
to  enable  the  seedling  to  escape  uninjured  from  the  testa,  on  whose 
protection  it  has  so  long  depended. 

Penetration  of  the  soil  may  be  either  from  above  or  from  below. 
When  seeds  are  scattered  on  the  surface  of  the  soil  they  are  enabled 
to  gain  a  foothold  in  the  earth  by  various  contrivances  so  that  the 
roots  may  be  sent  down  into  the  soil.  In  the  case  of  buried  (planted) 
seed  the  process  of  penetration  not  only  has  to  do  with  sending 
down  roots,  but  the  seed  must  find  a  way  out  of  the  earth,  un- 
harmed by  its  passage.  This  latter  problem  is  solved  most  often 
by  the  plantlet  being  started  from  the  seed  in  an  arched  position. 
One  end  of  the  arched  stem  takes  hold  of  the  ground  and  sends 
out  roots,  while  the  other,  attached  to  the  wide  cotyledons  or  the 
delicate  plumule  leaves,  gently  pulls  these  through  the  ground 
after  the  growing  arch  has  broken  away  to  the  surface.  If  forced 
directly  upward  these  bulky  appendages  would  be  stripped  off 
by  soil  pressure. 


GERMINATION  —  THE   SEED   WAKES  UP 


43 


This  arch  may  be  caused  by  the  weight  of  the  cotyledons  and 
soil  (as  in  the  case  of  the  bean),  which  hold  back,  the  bulky  end 
of  the  plantlet  until  the  stem  is  strong  enough  to  lift  it  out  of  the 


I.      Z.    3. 


C  —  COTYUEDOMS 
H  —  HYFOCOTVI. 
F  — "PLUMULE. 
&—  L  —  CrRouNp    LINE 


GERMINATION 


ground,  or  (as  in  the  case  of  the  pea)  by  the  tip  of  the  plumule 
being  held  tightly  between  cotyledons  that  are  not  lifted  from 
the  ground  at  all.  In  the  latter  case  the  hold  of  the  cotyledons 


44  BIOLOGY  FOR  BEGINNERS 

weakens  after  its  store  of  food  has  been  partly  exhausted  and  the 
plumule  is  released. 

Another  method  of  penetrating  the  soil  is  found  in  the  corn 
and  in  general  by  those  plants  whose  first  leaves  are  long  and 
slender.  In  these  cases  protection  is  secured  by  the  leaves  being 
tightly  rolled  into  a  point  and  covered  by  a  cap,  so  that  they 
pierce  the  soil  directly,  thus  meeting  less  resistance  and  securing 
safety. 

The  lifting  force  of  germinating  seeds  is  seldom  noticed,  but  is 
very  great.  Masses  of  earth  a  hundred  times  their  weight  are 
lifted  by  our  tiny  garden  seedlings  as  they  come  up,  forcing  their 
way  through  the  hardest  soil. 

The  last  and  most  important  step  in  germination  is  the  establish- 
ment of  the  young  plant  in  its  new  environment.  In  describing 
this  process  it  is  necessary  to  treat  of  the  development  of  each 
part  of  the  embryo  by  itself. 

The  hypocotyl  first  penetrates  the  testa.  Protected  by  its  root 
cap  and  directed  downward  by  gravitation,  it  begins  at  once  the 
production  of  the  primary  root  from  its  lower  end.  From  this, 
in  turn,  the  whole  root  system  rapidly  develops.  The  only  region 
of  growth  is  just  back  of  the  tip,  which,  protected  by  the  cap,  is 
safely  pushed  downward  into  the  earth. 

The  cotyledons,  as  before  explained,  may  rise  above  ground  if 
the  hypocotyl  lengthens  upward,  or,  if  not,  may  remain  below. 
In  either  case  they  act  as  a  storage  of  food  for  the  seedling. 

The  development  of  the  plumule  usually  attracts  most  attention 
for  from  it  arise  the  leaves,  stem,  and,  later,  the  flowers  and  fruit. 
It  constitutes  the  shoot  of  the  plant. 

The  first  organ  to  develop  in  germination  is  the  root,  because 
the  function  required  by  the  seedling  is  the  absorption  which  the 
root  performs.  We  shall  take  up  the  study  of  this  important 
organ  in  the  next  chapter. 

Many  of  the  statements  made  in  this,  and  the  preceding  chapter, 
can  be  proven  by  simple  experiments. 

In  the  first  place,  the  kind  of  foods  stored  in  the  seeds  can  be 
proven  by  the  tests  described  in  Chapter  IV. 


GERMINATION  —  THE   SEED  WAKES  UP  45 

The  Necessity  of  Stored  Foods.  The  necessity  of  this  stored 
food  can  be  shown  by  taking  a  number  of  well-started  seedlings, 
removing  part  of  the  stored  food  (in  cotyledon  or  endosperm)  in 
some  of  them,  removing  it  all  in  others,  and  leaving  still  others 
unharmed.  If  these  seedlings  are  then  placed  so  that  the  root  can 
dip  into  water,  by  suspending  them  on  a  netting  over  a  well-filled 
glass,  their  development  can  be  watched. 

Several  seedlings  must  be  used  in  each  group,  lest  we  draw 
conclusions  from  too  few  instances,  or  perhaps  be  misled  in  case 
some  one  seed  were  abnormal.  The  conditions  of  growth  must 
be  the  same  in  each  case,  lest  it  appear  that  these  varying  condi- 
tions, and  not  the  loss  of  stored  food,  produces  the  results. 

After  a  few  days  it  will  be  seen  that  the  whole  seeds  grow  well 
and  rapidly;  that  those  with  part  of  their  food  removed  start 
more  slowly  and  soon  cease  growing;  while  those  with  all  the  stored 
food  removed  scarcely  start  at  all.  This  is  because  of  the  fact 
that,  until  the  seedling  can  develop  roots  and  leaves,  it  depends 
solely  on  this  store  of  food  whose  removal  is  shown  to  have  so 
serious  results. 

The  Digestion  of  Stored  Foods  in  Seeds.  To  prove  that  these 
food  stuffs  must  be  digested  before  they  can  be  used  in  germinating 
plants,  corn  seeds  can  be  tested  for  starch  and  for  grape  sugar, 
both  before  and  after  germination  has  started. 

Starch  is  insoluble  in  cold  water,  and  does  not  pass  readily 
through  the  absorbing  membranes.  Therefore  it  has  to  be  digested 
(changed  to  soluble  sugars)  before  the  plant  can  use  it. 

This  digestive  change  is  accomplished  by  a  substance  in  the 
seed,  called  diastase,  which  acts  somewhat  like  the  digestive 
fluids  in  our  bodies. 

If  the  corn  be  tested  before  germination  has  begun,  much  starch 
and  little  or  no  sugar  will  be  found.  If  it  be  tested  in  the  same  ways, 
after  germination  has  proceeded  for  a  few  days,  the  reverse  will 
be  discovered,  as  most  of  the  stored  starch  will  have  been  converted 
into  soluble  form,  sugar,  by  the  diastase  in  the  cotyledon. 

Conditions  for  Germination.  That  sufficient  heat,  air,  and 
moisture  are  essential  conditions  for  germination,  can  be  proved 


46  BIOLOGY  FOR  BEGINNERS 

by  setting  up  experiments  in  which  several  seeds  are  given 
similar  treatment,  except  that  one  of  these  factors  is  changed  in 
each. 

To  prove  the  necessity  of  air,  place  several  seeds  in  each  of  two 
bottles,  give  them  moist  moss  to  grow  in,  and  keep  in  places  of 
similar  temperature.  Seal  one  tightly  and  leave  the  other  open. 
The  results  show  that  the  sealed  seeds,  though  they  start  growth, 
cease  as  soon  as  the  air  in  the  bottle  is  used  up,  while  those  in  the 
open  bottle  grow  naturally.  In  this,  as  in  all  experiments,  several 
seeds  should  be  used,  so  as  to  prevent  drawing  a  false  conclusion 
from  incomplete  evidence.  Using  many  seeds  and  repeating  the 
same  experiment  increases  the  accuracy  of  the  test.  Emphasis 
must  also  be  placed  upon  giving  the  same  conditions,  with  the  one 
exception,  in  every  case.  In  the  above  experiment,  if  the  seeds 
are  not  kept  in  places  of  similar  temperature  and  moisture,  the 
result  of  the  experiment  might  be  attributed  to  the  differences  in 
these  factors  and  not  to  the  presence  or  absence  of  air. 

In  the  same  way,  it  can  be  proved  that  seeds  require  a  definite 
amount  of  moisture  for  germination.  If  none  be  supplied,  or  if 
they  be  completely  covered  with  water,  most  seeds  will  not  grow 
even  when  the  air  supply  and  temperature  are  properly  regulated. 

A  similar  experiment  may  be  used  to  show  the  effect  of  tempera- 
ture on  seed  growth.  Arrange  several  seeds  in  each  of  three  or 
four  bottles;  give  the  same  amount  of  moist  moss  to  grow  in,  and 
expose  all  to  free  air  supply.  The  one  condition  to  be  varied  is 
the  temperature.  It  will  be  found  that  those  in  extreme  cold 
usually  do  not  start  growth  at  all,  those  in  very  warm  places  usually 
decay,  and  only  those  in  a  moderate  temperature  germinate 
naturally. 

Suppose  some  of  these  last  sets  of  seeds  had  been  given  vary- 
ing amounts  of  moisture  as  well  as  different  temperatures,  what 
ob'ection  could  be  raised  to  the  conclusion  given? 

Experiments  like  those  above  in  which  no  air  or  water  or  warmth 
were  supplied  and  in  which  no  results  occurred  are  sometimes 
called  "  check  "  experiments.  They  are  very  important,  as  show- 
ing that  a  certain  result  will  not  occur  without  certain  conditions. 


GERMINATION  —  THE  SEED  WAKES  UP  47 

which  is  often  as  necessary  as  proving  that  it  will  occur  with  certain 
others. 

Heat  Energy  and  Carbon  Dioxide  Set  Free.  It  has  been  stated 
in  Chapter  II  that  all  living  things  breathe.  This  means  that  they 
take  in  oxygen,  which  oxidizes  their  tissues,  produces  energy,  and 
liberates  carbon  dioxide  as  a  waste  product.  We  readily  realize  this 
in  the  case  of  animals  but  with  plants  it  needs  experimental  proof. 

Provide  two  large-mouthed  bottles  each  with  some  moist  moss, 
a  vial  of  lime  water,  and  a  stopper  through  which  is  inserted  an 
accurate  thermometer.  In  one  of  them  put  a  handful  of  soaked 
seeds  and  leave  the  other  with  none. 

As  the  seeds  begin  to  grow  it  will  be  observed  that  the  thermom- 
eter in  that  bottle  stands  higher  than  in  the  one  with  no  seeds,  also 
that  the  lime  water  in  the  seed  bottle  is  much  more  milky,  which 
proves  the  presence  of  more  carbon  dioxide.  The  lime  water  in 
the  seedless  bottle  is  slightly  milky  due  to  the  carbon  dioxide 
present  in  the  air.  Without  this  check  experiment,  nothing  could 
be  proved,  as  the  rise  of  temperature  could  not  be  compared 
and  the  presence  of  the  carbon  dioxide  could  be  attributed  to  that 
known  to  be  in  the  air.  Moss  was  put  in  both  bottles  so  that  all 
conditions  should  be  the  same ;  if  this  had  not  been  done,  it  might 
have  been  objected  that  the  presence  of  the  wet  moss  affected 
the  temperature  or  gave  off  carbon  dioxide. 

While  plants  do  not  breathe  as  actively  as  animals,  still  it  is 
thus  proved  that  they  do  breathe  in  the  same  way  and  for  the 
same  purpose,  namely,  to  liberate  energy  for  life.  The  fact  that 
they  are  less  active  and  need  less  energy  accounts  for  less  evidence 
of  their  breathing. 

SUMMARY 

The  seed,  a  stage  of  rest,  not  stoppage  of  life. 
Value  of  this  resting  stage: 

Dispersal  1  g         toward  reproduction. 

Protection  over  winter  J 

Germination  (resumption  of  active  growth). 
Conditions  for  germination: 

Moisture  —  Air  supply,  why  necessary  —  experimental  evidence. 
Heat  — Stored  food 


48  BIOLOGY   FOR  BEGINNERS 

Stages  in  germination: 

1.  Emergence  from  seed  coats. 

Adaptations,  Micropyle,  Cap  on  hypocotyl. 

2.  Penetration  of  soil. 

Adaptations. 

By  arching  method  caused  by 

(1)  Soil  pressure  (bean) . 

(2)  Cotyledon  pressure  (pea). 

By  direct  piercing. 

(1)  By  rolled  plumule  with  a  sheath  as  in  corn. 

3.  Obtaining  nourishment. 

(1)  From  stored  food  in  cotyledons. 

(2)  "  "      "    endosperm. 

(3)  Obtained  directly  by  leaf-like  cotyledons  (squash),  roots  from 

hypocotyl,  development  of  plumule  leaves. 

NOTE.  —  If  the  hypocotyl  does  not  lengthen  upward,  the  cotyledons 
must  remain  below  ground;  if  it  does  lengthen  the  cotyledons  "come  up." 
Cotyledons  may  store  food  below  ground  or  above;  they  may  become 
true  leaves,  or  merely  act  as  absorbing  organs.  (Give  an  example  of  each.) 

Experiments  to  show: 

1.  The  kind  of  food  stuffs  stored  in  seeds. 

2.  The  necessity  for  this  stored  food. 

3.  The  need  of  digestion  before  it  can  be  used. 

4.  The  necessity  of  air,  moisture,  and  warmth  for  germination. 

5.  That  growing  seedlings  produce  heat  and  carbon  dioxide  (that  is, 
that  they  breathe). 

COLLATERAL   READING 

Natural  History  of  Plants,  Kerner  and  Oliver,  Vol.  I,  p.  599;  Vol.  I 
(2),  pp.  598-623;  Vol.  II  (1),  pp.  420-427;  Lessons  with  Plants,  Bailey, 
pp.  336-341;  Lessons  in  Botany,  Atkinson,  pp.  210-216;  Studies  in  Plant 
Life,  Atkinson,  pp.  1-6;  Seeds  and  Seedlings,  Lubbock,  Vol.  I,  pp.  4-77; 
Textbook  in  Botany,  Gray,  pp.  9-27,  305-314;  The  Teaching  Botanist, 
Ganong,  pp.  161-190;  The  World's  Farm,  Gaye,  pp.  277-299. 

Lessons  with  Plants,  Bailey,  pp.  316-335;  Plant  Relations,  Coulter, 
pp.  138-141;  Botany  for  Schools,  Atkinson,  pp.  1-25;  Elementary  Botany, 
Atkinson,  pp.  307-313;  Experiments  in  Plants,  Osterhout,  pp.  69-86; 
Plants  and  Their  Children,  Dana,  pp.  75-98. 


CHAPTER  VIII 

ROOTS  — THEIR   STRUCTURE  AND  FUNCTION 

Vocabulary 

Constitute,  to  forri  part  of. 

Immersed,  covered  by  water. 

Adventitious,  growing  at  unusual  places. 

Retain,  to  hold. 

Epidermis,  the  outer  layer  of  plant  or  animal  tissues. 

Cortex,  a  spongy  layer  under  the  epidermis  of  roots. 

Cambium,  region  of  active  growth  in  root  or  stem. 

The.  developing  seedling  consists  primarily  of  the  root  and 
the  shoot.  The  latter  bears  the  buds,  leaves,  flowers,  and  fruit, 
while  the  root,  usually  hidden  and  unnoticed  in  the  soil,  plays  an 
equally  important  part  in  furnishing  food  and  stability  to  the 
plant. 

Characteristics  of  Roots.  The  root  differs  from  the  stem  in  the 
following  points: 

Root  Stem 

Bears  no  leaves  or  flowers.  Bears  leaves  and  flowers. 

Grows  irregularly.  Grows  by  definite  nodes. 

Growth  mostly  at  tip.  Growth  in  each  internode. 

Tip  protected  by  cap.  Tip  protected  by  scales. 

Branching  very  irregular.  Branching  regular. 

Turns  toward  gravity.  Turns  away  from  gravity. 

Branches  start  internally.  Branches  external. 

Root  System.  When  a  plant  is  pulled  from  the  soil,  the  root 
system  is  exposed.  This  may  consist  of  one  long  central  portion, 
the  primary  root,  from  which  many  secondary  branches  grow; 
or  it  may  be  a  fibrous  mass  of  small  roots  with  no  apparent  primary, 

49 


50  BIOLOGY  FOR  BEGINNERS 

as  in  most  grasses.  In  either  case  the  soil  particles  are  closely 
held  to  the  root  by  tiny  root  hairs,  the  active  agents  in  absorption 
which  are  adapted  to  take  up  the  thin  film  of  water  that  surrounds 
all  soil  particles. 

While  the  form  of  the  root  system  varies  greatly,  according  to 
the  kind  of  plant,  soil,  and  climate,  yet,  in  general,  all  roots  have  a 
very  similar  internal  structure,  as  is  shown  by  a  study  of  sections 


FIG.  8.     Section  of  corn  root,  showing  root  hairs  formed  from  elongated 
epidermal  cells.     From  Atkinson. 

of  roots  in  the  laboratory.  The  tips  of  young  roots,  split  length- 
wise and  dyed,  so  as  to  make  their  structure  plain,  should  be  used 
for  the  purpose. 

Internal  Structure.  A  typical  root  has  a  single  outer  layer,  the 
epidermis,  composed  of  thin-walled,  brick-shaped  cells,  from  which 
extend  innumerable  outgrowths  called  root  hairs.  Beneath  the 
epidermis  is  a  thicker  layer  of  thin- walled,  loosely  packed,  roundish 


ROOTS  — THEIR  STRUCTURE  AND   FUNCTION        51 

cells,  the  cortex.  This  is  separated  by  a  boundary  layer  from  the 
central  cylinder  which  occupies  the  remainder  of  the  root. 

In  this  central  cylinder  there  are  three  sorts  of  tissues  which 
are  also  found  in  stems,  though  differently  arranged.  They  are: 
(1)  wood  and  ducts,  (2)  bast,  (3)  cambium. 

The  woody  tissue  is  composed  of  thick-walled,  hard  cells  which 
give  strength  to  the  root  but  carry  little  sap,  and  ducts,  which  are 
long,  tubular  cells,  used  principally  for  the  transfer  of  sap  upwards 
toward  the  stem. 

The  bast  tissue  consists  of  tough,  fibrous  cells,  interspersed 
with  tubular  ones.  Its  function  is  both  to  give  toughness  and  to 
carry  sap  downwards. 

The  cambium  is  the  most  remarkable  tissue  in  the  plant.  It 
consists  of  thin-walled,  very  active  cells,  full  of  living  protoplasm 
which  have  the  power  of  rapid  growth.  In  fact,  all  growth  of 
the  plant  occurs  here,  and  if  the  cambium  be  destroyed,  the  plant 
will  die. 

Since  these  tissues  extend  into  the  stem,  where  we  will  hear  of 
them  again  when  we  study  stem  structure,  it  is  important  that  we 
should  remember  their  function  in  the  root. 

The  wood  and  ducts  are  generally  grouped  in  four  areas  near  the 
center,  and  alternating  with  them,  though  outside,  is  found  the 
bast.  The  cambium  forms  a  more  or  less  complete  ring  between 
the  two.  This  arrangement  permits  the  soil  water  to  reach  the 
ducts  without  mixing  with  the  digested  food  brought  down  from 
the  leaves  by  the  bast. 

Around  the  tip  of  each  growing  root  and  extending  up  a  little 
way  along  each  side  is  the  protective  root  cap,  composed  of  loose 
cells  easily  rubbed  off  without  allowing  injury  to  the  sensitive  tip 
as  it  pushes  through  the  soil.  The  region  of  most  active  growth, 
being  back  of  this  cap,  is  protected  from  injury,  as  would  not  be 
the  case  if  located  at  the  extreme  tip. 

Function  of  Root  Parts.  The  function  of  the  epidermis  and  its 
root  hairs  is  mainly  absorptive.  The  cortex  absorbs,  retains,  and 
transfers  the  soil  water;  the  ducts  and  bast  tubes  transfer  liquids 
and  air,  while  fibers  in  both  bast  and  wood  give  toughness  and 


52 


BIOLOGY  FOR  BEGINNERS 

fi.r**<r     7?o«r 


FIG.  9.     Root  Structure. 

Figure  1.  A  Fleshy  Root.  —  In  this  diagram  can  be  seen  the  general  region 
of  a  typical  root,  so  enlarged  by  food  storage  as  to  be  easily  visible  to  the 
naked  eye. 

Note  especially  the  ducts  in  the  central  cylinder,  from  which  extend 
secondary  branch  roots,  penetrating  the  cortex,  but  not  connecting  with  it. 
Where  they  come  out  they  make  the  tiny  cavities  characteristic  of  the  surface 
of  a  carrot  or  parsnip. 

See  also  that  the  stem  is  mainly  connected  with  the  ducts  of  the  central 
cylinder,  and  not  with  the  cortex  which  is  mainly  an  outer  layer  of  stored  food. 

Figure  2.  Root  Tip.  —  Here  is  shown  the  general  structure  of  a  root  tip 
under  low  power  magnification; —  these  parts  can  be  seen  on  any  growing  root 
from  germinating  seed. 

Note  the  protective  root  cap,  and  back  of  that  a  region  without  root  hairs 
which  includes  the  growing  point.  The  root  hairs,  if  developed  here,  would 
be  torn  off  as  growth  proceeded,  hence  begin  to  grow  further  back  from  the  tip. 

The  root  hairs  are  infinitely  numerous,  and  only  a  few  are  shown  to  indi- 
cate their  comparative  length  and  thinness  of  wall,  and  how  they  develop 
from  epidermal  cells. 

The  central  cylinder  and  cortex  can  be  distinguished  in  such  a  root,  es- 
pecially if  it  be  left  in  a  red  ink  solution  till  the  ducts  have  begun  absorption, 
which  makes  the  central  cylinder  much  darker  than  the  cortex. 

Figure  3.  The  Root  Tip  in  detail.  —  This  shows  the  extreme  tip,  much  more 
highly  magnified.  The  separate  cells  show  plainly,  and  those  near  the  grow- 
ing points  are  particularly  full  of  protoplasm  and  have  large  nuclei,  showing 
that  they  are  in  active  growth. 

The  loose  cells  of  the  cap  have  few  nuclei  and  are  largely  dead  cells,  thrown 
off  as  protection  to  the  delicate  tip. 

The  ducts  begin  to  show  as  thicker  rows  of  cells  though  not  very  tubular 
at  this  stage. 

The  epidermis  shows  plainly  as  a  single  layer  of  cells  packed  in  like  bricks. 


ROOTS  — THEIR  STRUCTURE  AND   FUNCTION        53 

strength.  The  most  important  function,  however,  is  performed 
by  the  cambium,  which  is  the  region  of  active  growth,  and  from 
which  both  wood  and  bast  are  produced. 

Functions  of  Roots  as  a  Whole.  Absorption.  The  root,  as  is 
evident  from  its  structure,  is  primarily  an  absorbing  organ,  and 
this  function  will  be  taken  up  at  length.  However,  it  has  many 
other  uses  and  is  adapted  to  perform  very  different  duties  in 
different  plants. 

Fixation.  A  second  use,  common  to  nearly  all  roots,  is  that  of 
attaching  the  plant  to  the  soil,  and  holding  it  in  an  upright  position. 

Storage.  Frequently  the  root  has  sufficient  bulk  to  act  as  a  very 
efficient  storage  place  for  foods.  This  is  particularly  important 
for  plants  that  retain  life  through  long  winter  months. 

Propagation.  It  may  happen  that  enough  nourishment  is  stored 
so  that  the  plant  can  send  up  shoots  at  various  places  or  even 
be  divided,  so  reproducing  the  plant. 

Adaptations  of  Root  Form.  From  the  foregoing  it  is  evident 
that  roots  must  be  profoundly  varied  in  structure  and  form  to 
perform  the  different  functions  mentioned.  And  it  must  be  re- 
membered that  not  only  function,  but  other  factors  such  as  climate, 
soil,  moisture,  and  exposure,  which  together  make  up  the  plant's 
environment,  affect  growth.  We  shah1  learn  that  only  so  far  as  a 
plant  is  fitted  to  its  environment  will  it  thrive. 

Kinds  of  Roots.  The  usual  place  from  which  roots  develop  is 
the  lower  end  of  the  hypocotyl.  Such  roots  are  called  normal  roots. 
If  they  grow  from  other  places  such  as  the  stem,  leaves,  or  upper 
part  of  the  hypocotyl,  they  are  called  adventitious  roots. 


NORMAL  ROOTS 

Soil  Roots.  Of  all  forms  of  normal  roots,  the  commonest  are 
the  soil  roots  and  these  are  of  many  kinds,  depending  upon  what 
functions  they  must  perform  and  the  character  of  the  soil,  moisture, 
or  climate  that  surrounds  them.  They  in  turn  may  be  divided 
into  three  general  classes. 

Fibrous  Roots  are  made  up  of  many  fine  slender  rootlets,  giving 


54  BIOLOGY  FOR  BEGINNERS 

large  extent  of  surface  for  absorption.  The  roots  of  the  grasses, 
for  instance,  are  so  numerous  that  they  hold  the  soil  together, 
forming  a  compact  layer  called  the  "  turf." 

Tap  Roots  are  greatly  enlarged  primary  roots  which  enable  the 
plant  to  go  deep  after  water  supply  and  hold  firmly  in  the  ground. 
The  thistle,  dandelion,  burdock,  and  many  more  of  our  worst 
weeds  are  thus  adapted  to  make  a  living  under  adverse 
circumstances. 

Fleshy  Roots  are  adapted  for  storage  of  food  stuffs  and  have  the 
main  part  greatly  thickened,  as  in  the  carrot,  turnip,  and  beet. 
They  are  generally  found  in  plants  which  require  two  seasons 
to  mature  their  seed  and  so  need  stored  food  to  carry  them  over 
the  winter.  In  other  cases,  as  the  dahlia  and  sweet  potato,  the 
fleshy  root  is  used  to  reproduce  the  plant. 

Aerial  Roots.  Some  tropical  orchids  which  live  attached  to 
trees  and  never  reach  the  earth  at  all  develop  aerial  roots.  They 
have  a  very  thick,  spongy  cortex,  which  absorbs  water  from  the 
moist  ah*  of  the  forests. 

Aquatic  Roots.  These  are  found  in  a  few  floating  plants  such 
as  the  duck- weed  and  water  hyacinth.  They  are  usually  small, 
few  in  number,  and  lacking  hi  root  hairs.  They  do  not  need 
extra  surface  for  absorption  because  they  are  surrounded  by  an 
abundant  water  supply. 

ADVENTITIOUS  ROOTS 

Brace  Roots.  From  the  stems  of  corn  and  many  other  grasses, 
develop  brace  roots,  which  help  to  support  the  slender  stems  or  to 
raise  them  again  if  they  are  bent  down. 

Roots  for  Propagation.  In  certain  plants  if  the  stem  lies  in 
contact  with  the  soil  for  a  sufficient  length  of  time,  roots  will 
spring  from  the  joints  and  produce  new  plants.  The  stems  of 
various  berry  bushes  can  thus  be  fastened  to  the  earth  —  "  staked 
down  "  —  and  will  take  root  in  this  way.  The  new  root  systems, 
when  sufficiently  developed,  can  be  separated  from  the  parent 
plant  to  make  a  new  berry  bush. 


ROOTS  — THEIR  STRUCTURE  AND   FUNCTION        55 

Slips  or  cuttings  from  certain  plants  develop  adventitious  roots 
from  the  stem  or  leaves  and  start  new  plants  by  this  means.  Many 
plants,  like  the  strawberry,  send  out  horizontal  stems  called 
"  runners  "  from  which  adventitious  roots  develop  and  produce 
other  individuals. 

Climbing  Roots.  The  stems  of  poison  ivy,  trumpet  creeper, 
and  some  other  vines  grow  climbing  roots  which  act  chiefly  as 
means  of  support.  These  plants  have  ordinary  soil  roots,  also, 
for  the  purpose  of  absorption. 

Parasitic  Roots.  In  a  few  plants,  such  as  the  dodder  and  mistle- 
toe, parasitic  roots  develop  from  the  stem,  penetrate  into  the 
tissue  of  some  other  plant,  and  absorb  food  from  their  victim, 
often  causing  its  death  or  serious  injury.  The  dodder  is  parasitic 
upon  clover,  golden-rod,  and  other  plants;  the  mistletoe  usually 
grows  upon  the  oak. 

REFERENCES   FOR   COLLATERAL   READING 

Natural  History  of  Plants,  Kerner  and  Oliver,  Vol.  I,  Part  1,  pp.  82-99; 
Part  2,  pp.  749-767;  Textbook  of  Botany,  Gray,  pp.  27-33;  The  World's 
Great  Farm,  Gaye,  pp.  124-128;  Plant  Relations,  Coulter,  pp.  89-108; 
Elementary  Studies  in  Botany,  Coulter,  pp.  253-270;  Plant  Life  and  its 
Uses,  Coulter,  pp.  123-141;  Experiments  in  Plants,  Osterhout,  pp.  87-162; 
Plants  and  their  Children,  Dana,  pp.  99-112;  Outlines  of  Botany,  Leavitt, 
pp.  36-45;  Botany  all  the  Year  Round,  Andrews,  pp.  120-142;  First 
Course  in  Biology,  Bailey  and  Coleman,  pp.  32-48;  Civic  Biology,  Hunter, 
pp.  71-83. 

Characteristics  of  Roots: 

1.  No  leaves,  or  flowers. 

2.  Growth  back  of  tip,  not  at  nodes. 

3.  Root  cap  for  protection,  instead  of  bud  scales. 

4.  Irregular  branching. 

5.  Turn  towards  gravity  —  against  light. 

6.  Internal  structure. 

Root  system  consists  of 

Primary  root,  or  fibrous  roots. 
Secondary  roots. 
Root  hairs. 


56 


BIOLOGY  FOR  BEGINNERS 

INTERNAL   STRUCTURE 


Part 

Structure 

Function 

1.   Epidermis 

Thin,  brick  shape 

Protection 

Root  hairs 

Thin,    tubular,    sensi- 

Absorption 

tive 

2.   Cortex 

Loose,  thin,  round 

Transfer 

Storage 

3.   Central  cylinder 

Wood 

Thick,  fibrous 

Support 

Ducts 

Thick,  tubular 

Transport 

Bast 

Thin,  tubular 

Transport 

Cambium 

Delicate,  active 

Growth 

4.    Root  cap 

Loose,  thin  cells 

Protection 

Region  of  growth. 
Functions  of  roots : 

Absorption  (most  roots). 
Fixation  in  soil  (most  roots). 
Storage  (carrot,  etc.). 
Propagation  (hop,  dahlia,  etc.). 
Modification  of  Roots: 

Caused  by  difference  in 
Function. 
Climate. 
Soil. 


Moisture. 

General  surroundings. 

Exposure. 


KINDS  OF  ROOTS 


Normal  forms 

Examples 

Adapted  for 

1.  Soil  Roots 
(a)  Fibrous 
(6)  Tap-root 
(c)   Fleshy 
2.   Aerial 
3.  Aquatic 

Grass 
Dandelion 
Carrot 
Orchid 
Duck-weed 

Wide  surface 
Deep  water  supply 
Storage 
Absorption  from  air 
Absorption  from  water 

ADVENTITIOUS  FORMS 


1.  Brace-roots 
2.  Propagation 
3.  Climbing  roots 
4.  Parasitic 

Corn 
Strawberry 
Poison-ivy 
Dodder 

Support 
Reproduction 
Support,  climbing 
Stealing  nourishment 

ROOTS  — THEIR  STRUCTURE  AND   FUNCTION        57 
Adaptations  of  Roots: 

For  penetration  of  soil: 

1.  Protective  cap. 

2.  Growing  point  back  of  tip,  for  protection. 

3.  Root  hairs  back  of  tip,  for  protection. 

4.  Geotropism  and  hydro tropism  (see  next  chapter). 

For  storage: 

1.  Large  size. 

2.  Protection  in  soil  from  cold,  drought,  and  animals. 

3.  Poisonous  or  bad  tasting,  to  protect  from  animals. 

For  support: 

1.  Depth  and  extent  of  root  system. 

2.  Toughness  of  wood  and  bast  fibers. 

3.  Special  brace  roots,  climbing  roots,  etc. 

NOTE.  —  Look  up  cypress  "knees,"  and  adventitious  roots  of  banyan  tree. 


CHAPTER  IX 

ABSORPTION  AND   OSMOSIS 

Vocabulary 

Gravitation,  the  attraction  of  the  earth  which  draws  everything 

downward. 

Successive,  one  after  another. 
Aerial,  living  in  the  air,  as  applied  to  roots. 
Hydrotropism,  the  response  of  plant  parts  to  water. 
Geotropism,  the  response  of  plant  parts  to  gravitation. 
Osmosis,  the  diffusion  of  two  liquids  or  gases  through  a  membrane, 

the  greater  flow  being  toward  the  denser  substance. 
Turgescence,  the  support  of  plant  parts,  especially  leaves,  due  to 

the  presence  of  water  in  the  tissues. 

The  preceding  chapter  should  have  given  us  a  rather  definite 
idea  as  to  the  structure  of  roots,  and  the  names,  at  least,  of  some 
of  their  functions. 

This  chapter  deals  with  absorption,  the  most  important  function 
of  all,  since  it  is  one  of  the  principal  ways  in  which  plants  obtain 
food  materials.  We  shall  study  in  detail  the  adaptations  of  the 
root  for  this  fundamental  function. 

Necessity  of  Water  for  Plants.  All  living  matter  depends  more 
or  less  on  liquids  of  various  sorts,  and  the  plant,  like  the  animal, 
has  its  circulating  fluids,  bearing  nourishment  and  removing 
waste,  storing  food,  and  supplying  oxygen  to  convert  that  food 
into  living  energy. 

From  the  delicious  juices  that  flavor  the  peach  and  sweeten 
in  the  heart  of  the  sugar  cane,  to  the  bitter  milk  that  flows  in  the 
dandelion  or  lures  the  unwary  to  death  in  the  poisonous  mush- 
room, all  consist  largely  of  water,  absorbed  from  the  soil  by  the 
action  of  the  roots. 

This  absorbed  water  is  of  threefold  value  to  the  plant.  It 
supplies  a  very  necessary  portion  of  the  plant's  food,  as  water 

58 


ABSORPTION  AND   OSMOSIS  59 

itself  and  as  mineral  matter  dissolved  in  that  water;  it  acts  as  a 
means  of  transfer  within  the  plant  for  the  various  foods  needed 
in  the  different  parts,  much  like  the  blood  of  animals;  and  this 
absorbed  water  supports'  many  parts  of  the  plant.  This  latter 
statement  will  need  some  explanation. 

Turgescence.  When  a  plant  is  deprived  of  water,  its  leaves 
droop  and  we  say  it  wilts.  This  is  due  to  the  fact  that,  normally, 
each  cell  is  expanded  by  the  water  within  it  and  so  is  kept  in  posi- 
tion. If  the  water  be  withdrawn,  these  cells  will  collapse  like  an 
empty  balloon,  allowing  the  leaves  and  plant  to  droop.  If  water 
be  supplied  before  the  protoplasm  dies,  however,  the  leaves  and 
plant  will  resume  position. 

This  stiffness  of  plants,  due  to  presence  of  water,  is  called  tur- 
gescence  and  is  very  important  in  supporting  the  smaller  plants 
whose  stems  are  not  stiffened  with  wood  fibers.  Nearly  all  leaves 
depend  on  this  water  pressure  for  their  expansion. 

Osmosis.  The  water  to  supply  these  absolutely  essential  needs 
comes  from  the  soil,  often  apparently  dry,  but  always  containing 
at  least  a  little  moisture  which  the  plant  must  obtain  if  it  is  to  live. 

This  vastly  important  root  function  of  absorption  depends  on 
a  physical  process  called  osmosis  which  may  be  defined  as  the 
mixing  or  diffusion  of  two  liquids  or  gases  of  different  densities, 
through  a  non-porous  membrane  —  the  greater  flow  being  toward 
the  denser  substance.  Osmosis  is  one  of  the  most  important 
biologic  processes,  and  upon  it  depends  not  only  absorption  in 
roots,  but  all  forms  of  absorption  in  plant  and  animal,  all  digestive 
processes,  excretion,  respiration,  and  assimilation.  Wherever  a 
liquid  or  gas  passes  through  any  tissue,  osmosis  is  the  acting  cause, 
controlled  sometimes  by  the  living  protoplasm  that  lines  the  cell. 

The  essentials  for  osmosis  are  a  dense  liquid,  a  less  dense  liquid, 
and  the  osmotic  membrane.  In  the  root  the  wall  of  the  root  hair 
or  epidermal  cell  acts  as  the  membrane,  the  cell  sap  as  the  denser, 
and  the  soil  water  as  the  less  dense  liquid. 

Root  Hairs.  It  has  been  estimated  that  there  may  be  a  total 
length  of  a  mile  in  the  roots  of  a  corn  plant,  and  alfalfa  roots  have 
been  found  to  extend  twenty  feet  deep  in  dry  soil. 


60  BIOLOGY  FOR  BEGINNERS 

For  the  purpose  of  absorbing  as  much  as  possible,  the  surface 
of  the  active  parts  of  all  roots  is  covered  with  root  hairs.  These 
are  outgrowths  of  the  epidermal  cell  walls  and  increase  the  total 
absorbing  surface  enormously.  They  also  enable  the  osmotic 
membrane  to  actually  touch  the  film  of  water,  which,  even  in  the 
driest  soils,  clings  close  to  the  soil  grains. 

So  important  are  these  root  hairs  that  their  injury  or  loss  might 
mean  death  to  the  plant,  hence  they  are  never  borne  at  the  extreme 
tip  of  the  root,  where  its  growth  through  the  soil  would  strip  them 
off,  but  are  found  a  little  back  from  the  tip  and  extending  various 
distances  along  the  younger  roots. 

As  the  root  grows,  new  hairs  are  produced  near  the  tip,  to  gather 
moisture  from  new  areas;  the  upper  ones  die  away;  the  cortex 
and  epidermis  thicken,  cease  active  absorption,  and  become 
protective  in  use.  In  frequent  cases,  the  root  hairs  secrete  a  weak 
acid  which  helps  in  dissolving  soil  substances  and  in  penetrating 
hard  earth. 

The  adaptations  of  root  hairs  may  be  summarized  as  follows: 

1.   Extent  of  surface.  2.   Thinness  of  walls. 

3.  Protection  from  injury.  4.  Location. 

5.   Close  contact  with  soil  grains.  6.   Acid  secretion. 

Geotropism.  In  order  that  roots  may  always  grow  where  they 
can  best  absorb  food  materials,  they  show  a  tendency  always  to 
grow  downward,  i.e.,  toward  the  earth.  This  might  at  first  thought 
be  credited  to  mere  weight,  but  it  is  evident  that  stems,  though 
equally  heavy,  cannot  be  made  to  grow  down,  and  that  roots, 
though  lighter  than  the  soil,  still  force  their  way  through  it,  and 
cannot  be  made  to  grow  upward,  even  though  repeatedly  started 
in  that  direction. 

This  turning  of  roots  and  stems  is  caused  by  the  attraction 
of  the  earth,  called  gravitation,  and  this  response  that  plants 
make  to  gravitation  is  called  geotropism  —  positive  in  the  case  of 
roots,  and  negative  in  the  case  of  stems.  Positive  geotropism 
plays  an  essential  part  in  absorption  by  causing  the  roots  to  pene- 
trate the  soil  rather  than  grow  in  any  chance  direction. 


ABSORPTION  AND   OSMOSIS  61 

Hydrotropism.  Roots  respond  similarly  to  the  presence  of 
water,  turning  toward  moisture  even  at  long  distances.  This 
tendency,  called  hydrotropism,  is  very  useful,  especially  if  soil 
water  be  scant.  Vast  numbers  of  fine  roots  are  often  found  project- 
ing into  springs  and  streams,  forcing  their  way  into  water  pipes 
or  piercing  deep  into  the  soil,  led  by  this  force  that  turns  them 
toward  the  needed  moisture. 

Selective  Absorption.  Another  fact  connected  with  absorption 
is,  that  plants,  though  growing  side  by  side,  take  very  different 
matters  from  the  same  soil.  This  apparent  impossibility  is  ac- 
complished by  the  action  of  the  protoplasm  which  lines  the  inner 
walls  of  all  active  cells  and  has  the  remarkable  power  to  select, 
in  a  considerable  degree,  what  substance  the  roots  shall  absorb 
with  the  water.  This  selective  absorption,  as  it  is  called,  accounts 
for  the  variety  of  food  substances  taken  from  the  same  soil  by 
different  plants. 

Successive  Osmosis.  All  this  arrangement  for  absorption  would 
be  useless,  were  there  not  some  way  provided  for  passing  on  the 
absorbed  liquids  after  being  taken  up  by  the  root  hairs.  When 
the  outer  layer  of  cells  has  taken  in  soil  water  their  contents  are 
diluted,  and  they  become  less  dense  than  those  next  within.  Their 
contents  tend  to  pass  to  the  next  inner  layer,  as  the  osmotic 
current  is  always  toward  the  denser  liquid. 

This  last  step  removes  the  newly  absorbed  soil  water  from  the 
epidermal  cells  and  leaves  them  denser  again,  ready  to  absorb 
more  soil  water  from  without. 

Root  Pressure.  This  process  continues  inward,  from  cell  to 
cell,  till  the  ducts  are  reached,  when  the  liquids  rise  up  through 
root  and  stem,  causing  the  uplift  which  is  known  as  joot  pressure. 

This  root  pressure  is  one  important  cause  of  the  circulation  of 
sap  in  plants,  and  is  often  sufficient  to  raise  the  water  to  heights 
of  one  hundred  feet  or  more.  But  neither  this  nor  any  other  known 
cause  is  equal  to  the  task  of  lifting  water  as  high  as  some  of  our 
tallest  trees,  and  the  method  by  which  that  is  done  is  still  unknown. 
This  inward  osmosis  may  be  reversed  by  putting  salt  in  the  soil.  It 
dissolves  in  the  soil  water,  makes  it  denser  than  the  contents  of 


62 


BIOLOGY   FOR  BEGINNERS 


wer  MOSS 


the  cells,  which  are  therefore  robbed  of  their  water,  since  the 
osmotic  flow  is  toward  the  liquid  of  greater  density.  This  fact  is 
often  utilized  in  killing  weeds  and  grass  along  the  sidewalks. 

Variations  in  Osmosis.  Osmosis  hi  roots  is  affected  by  the 
temperature  and  amount  of  moisture  in  the  soil,  being  less  in  cold, 
dry  seasons.  Also  the  presence  of  organic  acids  in  bogs,  or  of 
certain  mineral  matters  in  some  soils,  tends  to  hinder  or  prevent 
the  process.  Hence  it  follows  that  in  our  cold  season,  most  plants 

shed  their  leaves,  so  that 

C-E  0  T8  0  P  /  5  ^  tnev  nave  ^ess  surface  fr°m 

~~  which  to  evaporate  water, 

because  their  supply  is  cut 
down  by  the  cold. 

In  the  case  of  both  bog 
and  desert  plants,  many 
schemes  to  retain  moisture 
have  developed.  Though 
in  such  different  surround- 
ings, both  classes  of  plants 
have  difficulty  in  absorbing 
enough  water,  because  of 
the  stoppage  of  osmosis. 

Aerial  roots  find  even 
greater  difficulty  in  obtain- 
ing sufficient  water,  and 
many  wonderful  devices 
have  been  developed  in 
FIG.  10.  Compare  the  position  of  root  the  way  of  hairs  to  radiate 

and  of  stem  in  A  and  B.  heat,  scales  to  catch  water, 

and    enormous,    thickened 

cortex  to  retain  it  when  once  it  is  absorbed. 

EXPERIMENTS  WITH  ROOTS 

To  Prove  that  Roots  turn  toward  Gravitation.  If  well-started 
seedlings  be  inserted  in  a  split  cork  which  is  then  put  into  a  test 
tube  of  water  and  inverted,  it  will  be  found  that  the  upward 


PLANT     INVERTE  O 

ROOT3     TURAHNfr    DOWM 
TURNING      UP 


(pQS  -) 


ABSORPTION  AND   OSMOSIS 


63 


pointing  root,  will  soon  turn  downward  at  the  tip,  as  will  all  of  its 
branches.  This  can  be  repeated  with  any  kind  of  seeds.  It  would 
not  do  to  infer  a  general  rule  from  one  or  two  cases. 

If  a  germinating  box  with  well-grown  seedlings  be  turned  on 
its  side,  the  roots  will  turn  down,  no  matter  how  often  the  experi- 
ment be  changed,  thus  proving  the  same  thing  in  another  way. 
Our    experience     with 
planting   seeds   in    the 
garden  also  is  a  good 
experiment  in  the  same 
line;     the    root    turns 
down,  no  matter  how 
the  seed  is  placed. 

The  same  experi- 
ments prove  that  stems 
turn  away  from  gravi- 
tation's pull.  This  is 
called  negative  geotro- 
pism,  and  applies  to 
most  plant  parts  except 
roots.  It  is  evident 
that  what  we  call 
"  weight  "  has  nothing  <* 

to  do  with  the  direction     5     s  EB os    IN 
of  either  root  or  stem.      <*• 


,. XX    ^>X         WET 

-=ST 


nojs 


•ROOT 


I 
i 

Cr 


BY 


INCLINED      SIEVE 

If     INFLUENCED 
ONLY 


FIG.  11.     Note  different   direction   taken 
roots,  when  attracted  by  moisture. 


by 


The  root,  though  not 
so  heavy  as  the  soil, 
penetrates  it  on  its  way 
downward,  and  the 

stem,  despite  its  weight,  turns  upward,  due  to  this  effect  of  gravita- 
tion on  all  the  living  cells. 

It  might  be  thought  that  light  had  something  to  do  with  this 
change  of  direction  in  plant  parts.  How  could  it  be  decided  by 
experiment? 

To  Prove  that  Roots  Turn  toward  Moisture.  If  seeds  be  planted 
on  the  bottom  of  a  coarse  sieve  which  is  then  filled  with  wet  moss 


64 


BIOLOGY  FOR  BEGINNERS 


and  tilted  at  an  angle  of  about  45  degrees,  the  direction  taken  by 
the  roots  will  be  different  from  what  might  have  been  expected 
from  the  above  experiment. 


. 
LIQ.UIO 


teas  DCft 

I.IOUIO 


SI/CrAft 

SOLUTION 


__. 


//v 

HOOT  -   N 


CELL     WALL 


SOt  L. 

i    WATE  K 


FIGS.  12  and  13.    Osmosis  in  root-hair.    Laboratory  experiment  to 
demonstrate  osmosis  of  liquids. 

The  roots  will  start  downward  at  first,  directed  by  gravitation, 
but  when  they  have  penetrated  the  sieve,  they  will  turn  toward 
it  again  and  reenter  the  moss  in  order  to  find  moisture. 


ABSORPTION  AND   OSMOSIS  65 

This  response  of  roots  to  moisture  is  called  hydrotropism,  and 
will  cause  roots  to  turn  toward  a  water  supply  if  the  surroundings 
be  dry,  even  though  they  turn  partly  away  from  the  direct  down- 
ward line. 

To  Demonstrate  Osmosis.  Fill  an  artificial  diffusion  shell  (such 
as  can  be  purchased  from  dealers  in  laboratory  supplies)  with 
molasses  and  fasten  it  tightly  to  a  long  glass  tube  by  wiring  it 
to  a  rubber  stopper.  Insert  the  shell  in  a  jar  of  water.  Here 
are  the  three  essentials  for  osmosis.  The  shell  is  the  osmotic 
membrane,  the  molasses,  the  dense  liquid,  and  the  water,  the 
less  dense  liquid. 

The  rise  in  the  tube  will  be  rapid  and  usually  reaches  a  height 
of  several  feet.  This  illustrates  in  a  way  the  action  of  a  root  hair 
in  causing  root  pressure,  though  the  root  hair,  because  of  its 
protoplasmic  lining,  selects  what  will  be  absorbed,  while  the 
apparatus  does  not. 

With  the  same  apparatus,  starch  or  proteid  or  fat  can  be  placed 
in  the  shell,  and  it  will  be  found  that  no  osmosis  goes  on,  and  that 
they  cannot  be  found  in  the  water  outside  the  diffusion  shell. 
On  the  other  hand,  the  sugar,  peptone,  or  other  soluble  food  stuff, 
will  pass  through  the  membrane,  and  can  be  found  by  test  in  the 
water  outside. 

Not  only  does  plant  absorption  depend  upon  osmosis  but  nearly 
all  the  life  processes  of  plants  and  animals  utilize  this  process  in 
some  degree,  as  will  be  seen  as  we  proceed. 

COLLATERAL    READING 

ABSORPTION 

Elementary  Botany,  Atkinson,  pp.  22-27;  Lessons  in  Botany,  Atkinson, 
pp.  36-44;  Physiological  Botany,  Gray  and  Goodale,  pp.  230-232;  Text- 
book of  Botany,  Bessey,  pp.  175-176;  The  Story  of  Plants,  Allen,  pp.  53-73; 
Introduction  to  Biology,  Bigelow,  pp.  41-45. 

GEOTROPISM 

Lessons  with  Plants,  Bailey,  p.  330;  How  Plants  Grow,  Bailey,  p. 
350;  Plant  Relations,  Coulter,  pp.  69,  89-91,  138-141;  Textbook  of  Botany, 
Stevens,  pp.  24,  43,  61,  114;  Plant  Structures,  Coulter,  pp.  303-309;  Ele- 
mentary Botany,  Atkinson,  pp.  82-84;  First  Studies  in  Plant  Life,  Atkinson, 


66 


BIOLOGY   FOR  BEGINNERS 


pp.  27-32;  Lessons  in  Botany,  Atkinson,  p.  108;  Textbook  of  Botany, 
Bessey,  pp.  194-196;  Nature  and  Work  of  Plants,  pp.  38-39,  74;  Natural 
History  of  Plants,  Kerner  and  Oliver,  Vol.  I,  Part  1,  pp.  88-90;  Textbook 
of  Botany,  Strasburger,  p.  254. 

HYDROTROPISM 

Plant  Relations,  Coulter,  pp.  89-93;  Plant  Structures,  Coulter,  pp.  307- 
309;  Elementary  Botany,  Atkinson,  p.  90;  Natural  History  of  Plants, 
Kerner  and  Oliver,  Vol.  I,  Part  2,  p.  775;  Physiological  Botany,  Gray, 
pp.  393-394;  Textbook  of  Botany,  Strasburger,  pp.  261-280;  Textbook  of 
Botany,  Stevens,  p.  102. 

OSMOSIS 
(See  references  at  end  of  Chapter  LIII.) 

SUMMARY 
Necessity  of  water. 

1.  Food. 

2.  Transportation  of  food,  mineral  matter,  etc. 
Transportation  of  oxygen. 
Transportation  of  waste. 

3.  Turgescence. 

Meaning  of  term. 
Where  it  is  active. 

Importance,  in  absence  of  woody  support. 
Osmosis. 

1.  Definition. 

2.  Processes  dependent  upon  osmosis: 

Absorption 

Assimilation 

Digestion 

Respiration 

Excretion 


Essentials  for  osmosis 

In  plant 

In  experiment 

Membrane 
Dense  liquid 
Less  dense  liquid 

Root  hair  or  cell  walls 
Cell  sap 
Soil  water 

Diffusion  shell 
Sugar  solution 
Water  in  bottle  . 

(Diagram  of  root  hair  —  of  experiment) 
Root  hairs. 

Structure  (see  diagram).     Location  back  of  tip. 
Adaptations  for  absorption. 


ABSORPTION    AND    OSMOSIS  67 

1.  Large  extent  of  surface. 

2.  Thin  walls  for  osmosis. 

3.  Location  for  protection  and  large  contact  with  soil. 

4.  Acid  secretion  to  dissolve  mineral  matter. 

Geotropism.     (Contrast  action  of  mere  weight.) 
Definition. 
An  adaptation  for 
Penetration  of  soil. 
Obtaining  water  in  soil. 
Obtaining  nourishment. 
Positive  in  roots. 
Negative  in  stems. 
Hydrotropism. 
Definition. 

Function,  reaching  water  supply. 
Selective  absorption. 

Meaning  of  term.     How  controlled. 
Successive  osmosis. 

Meaning  of  term.     Explanation. 
Root  pressure. 

Meaning  of  term.     Reverse  osmosis. 
Experiments  with  roots:    Geotropism;    Hydrotropism. 


CHAPTER  X 

STEMS:    THEIR  FORMS  AND  FUNCTIONS 

Vocabulary 

Node,  the  point  on  a  stem  at  which  a  leaf  is  attached. 
Inter-node,  the  space  between  the  nodes. 
Propagate,  to  reproduce  a  plant  or  animal. 
Terminal,  at  the  end. 
Lateral,  from  the  side. 
Deliberately,  intentionally. 

The  stem  is  all  that  portion  of  the  plant  body  above  the  root. 
It  differs  from  the  root  in  the  following  points: 

1.  It  bears  leaves,  flowers  and  fruit. 

2.  The  leaves  and  branches  are  borne  in  regular  order,  at  points 

called  nodes. 

3.  Growth    takes   place    in    the    spaces    between    the    nodes 

(internodes). 

Functions.   The  functions  of  the  stem  are: 

1.  To  expose  leaves  to  light  and  air. 

2.  To  support  flowers  for  pollenation. 

3.  To  support  fruit  for  dispersal.  .  • 

4.  To  transport  liquids  up  or  downward  in  the  plant. 

5.  To  connect  the  two  food-getting  organs,  roots  and  leaves. 

6.  To  store  food  stuffs. 

7.  To  propagate  the  plant. 

Naturally  there  are  many  adaptations  for  these  various  functions 
resulting  in  many  forms  of  stem  growth  and  structure,  which 
modify  the  whole  appearance  of  the  plant. 

.68 


STEMS,  THEIR  FORMS  AND   FUNCTIONS  69 

KINDS  OF  BRANCHING 

Due  to  Leaf  Arrangement.  (Opposite  and  Alternate)  The 
branches  of  the  stem  originate  as  buds,  which  may  be  at  the  end 
of  the  stem  (terminal),  or  at  the  nodes,  just  above  the  leaves 
(lateral).  Insomuch  as  the  branches  always  originate  in  this 
way,  it  follows  that  if  the  leaves  are  opposite  on  the  stem,  the 
branches  will  be  opposite  also,  and  if  the  leaves  are  alternately 
arranged,  the  branches  will  arise  in  the  same  order. 

Examples  of  opposite  arrangement  are  found  in  the  ash,  maple, 
and  horse-chestnut.  The  alternate  type  is  represented  by  the  elm, 
oak,  beech,  and  apple. 

In  either  case  the  chief  object  of  the  branch  arrangement  is  to 
expose  the  leaves  uniformly  to  light  and  air.  This  is  accomplished 
in  various  ways,  depending  upon  the  development  of  the  branch 
buds,  which  influences  the  shape  of  the  plant  even  more  than  the 
leaf  arrangement. 

Branching  Due  to  Bud  Development.  Excurrent.  If  the  termi- 
nal bud  keeps  in  advance  of  the  lateral  buds,  a  slender,  cone- 
shaped  outline  results,  called  the  excurrent  type,  such  as  is  shown 
in  the  pines  and  spruces. 

Such  trees  have  several  advantages: 

1.  They  grow  rapidly  above  their  neighbors. 

2.  Their  slender,  flexible  tops  offer  little  resistance  to  storms. 

3.  They  can  grow  close  together  and  still  let  light  down  to  the 

lower  branches. 

4.  Their  lower  branches  can  bend  and  shed  snow  easily. 

For  these  reasons  the  excurrent  type  is  particularly  adapted  to 
cold  northern  regions,  where  it  is  most  frequently  found. 

Deliquescent.  If,  on  the  other  hand,  the  lateral  buds  equal  or 
exceed  the  terminal  ones,  the  plant  assumes  a  broad  spreading 
outline  called  the  deliquescent  type  as  shown  by  the  elm,  apple, 
and  oak.  This  type  is  very  successful  in  competition  with  other 
forms,  because,  even  though  it  may  start  late,  its  broad  top  shades 
and  kills  its  neighbors.  All  plants  which  grow  mixed  with  these 


70  BIOLOGY  FOR  BEGINNERS 

broad-shouldered  and  broad-leaved  giants,  must  either  get  a  start 
before  the  leaves  come  in  the  spring  or  else  must  have  learned  to 
live  with  very  little  light. 

Forked  Branching.  Indefinite  Branching.  The  growth  of  the 
terminal  bud  may  be  checked  by  bearing  flowers.  If  so,  the  branch 
usually  forks  in  a  Y  shape,  producing  round-topped  plants,  such  as 
the  horse-chestnut  and  magnolia.  In  some  shrubs  the  terminal 
bud  is  unprotected  for  winter,  hence  is  killed  back  and  thus  produces 


FIQ.  14.     Creeping  stem  of  the  water  fern  (marsilia).    From  Atkinson. 

a  very  irregular  type  of  branching,  called  indefinite.    This  is  well 
illustrated  by  the  sumach. 

MODIFICATION  OF  STEMS 

As  would  be  expected,  stems  are  variously  adapted  to  suit 
different  conditions  and  functions,  thus  giving  rise  to  many  forms. 

Shortened  Stems.  In  some  plants  like  the  dandelion,  the  stern 
is  so  shortened  that  the  leaves  seem  to  come  in  a  rosette,  directly 
from  the  top  of  the  root.  On  this  account,  the  term  "  stemless  " 
is  sometimes  applied  to  such  cases.  These  low-growing  plants 
have  many  advantages,  among  which  may  be  mentioned : 


STEMS,  THEIR   FORMS  AND   FUNCTIONS  71 

1.  Escape  from  grazing  animals. 

2.  Escape  from  crushing  by  being  stepped  on. 

3.  Crowding  away  neighbors  by  the  wide,  close  leaves. 

4.  Water  is  retained  near  the  root,  by  the  cover  of  leaves  above. 
Creeping  Stems.     The  creeping  stem  is  another  type,  with 

common  examples,  such  as  the  strawberry,  in  which  a  plant, 
though  having  a  weak  and  slender  stem,  is,  with  great  economy 
of  wood  tissue,  enabled  to  spread  its  leaves  widely.  By  this  habit 
it  also  escapes  injury  from  wind,  cold,  or  storms,  since  it  is  closely 
attached  to  the  earth  at  frequent  intervals.  Besides,  these 
"  runners,"  as  the  horizontal  branches  are  called,  furnish  a  valuable 
means  of  propagation,  since  they  send  out  roots  at  the  nodes, 
and  grow  even  if  separated  from  the  parent  plant. 

Climbing  Stems.  Many  stems  succeed  in  exposing  their  leaves 
to  the  light  without  producing  much  more  supporting  tissue  than 
do  the  creepers.  These  are  the  climbing  stems  which  use  supports 
outside  of  their  own  structures  to  lift  themselves  into  the  light. 
One  means  of  climbing  is  by  twining  round  some  supporting  plant, 
as  in  case  of  hops  and  pole  beans.  Another  similar  method  is  by 
means  of  tendrils,  which  are  usually  leaves  reduced  to  the  mere 
skeleton  of  veins,  as  in  the  grape,  wild  cucumber,  etc. 

The  coiling  of  tendrils  or  twining  stems  is  a  curious  process, 
for  it  frequently  seems  as  though  a  plant  or  tendril  had  started 
straight  for  a  certain  support  and  deliberately  coiled  about  it. 
This  is  not  the  case  though  the  real  process  is  scarcely  less  wonderful. 
The  tip  of  the  twiner  or  the  tendril  grows  unequally  on  different 
sides,  causing  it  to  swing  through  the  air  in  circles,  as  it  grows. 
Thus  it  has  a  chance  to  reach  anything  within  the  radius  of  its 
swing,  which  is  often  several  inches. 

Having  reached  a  support,  the  growing  point  can  no  longer 
swing  as  a  whole,  but  the  tip  coils  about  the  support  as  it  grows, 
enabling  it  to  rise  as  high  as  its  sturdier  neighbors.  Tendrils  also 
coil  between  the  support  and  the  plant,  raising  the  latter  and  hold- 
ing it  by  a  spring  which  will  yield  to  wind  pressure  without  break- 
ing. This  later  coil  usually  reverses  midway  to  avoid  twisting  the 
tendril  off. 


72  BIOLOGY  FOR  BEGINNERS 

Other  methods  of  climbing  are  found  in  plants  like  the  poison 
ivy,  which  produces  adventitious  roots  to  attach  itself,  and  in  the 
nasturtium,  which  climbs  by  hooking  its  leaf  stalks  around  the 
supports. 

In  any  case,  the  climbing  habit  is  very  successful,  especially  in 
crowded  tropical  forests  where  the  shade  renders  necessary  some 
means  for  a  slender  plant  to  reach  up  into  the  light  to  display  its 
leaves.  This  the  climbers  do  with  least  possible  outlay  of  wood  tissue. 

Fleshy  Stems.  Another  modification  of  stems  which  frequently 
occurs  is  developed  for  the  storage  of  food.  The  stem  assumes  a 
fleshy  form,  allowing  a  large  storage  volume  with  little  exposure 
of  surface.  Such  fleshy  stems  are  usually  developed  underground 
in  order  to  protect  their  stored  food  from  animals  and  cold.  Like 
the  fleshy  root,  these  underground  stems  enable  the  plants  to  get 
an  early  start  in  spring  and  also  often  propagate  the  plant  very 
successfully.  The  simplest  underground  stem  is  the  root  stock 
found  in  sweet  flag  and  Solomon's  seal.  Other  common  forms  are 
the  tuber  of  the  potato,  and  the  bulbs  such  as  the  onion,  lily,  tulip, 
etc.  It  may  seem  hard  to  think  of  these  as  stems,  yet  if  we  turn 
to  the  first  paragraph  of  this  chapter,  we  will  find  that  they  have 
the  characteristics  mentioned  there  and  are  merely  modified  to 
adapt  them  to  special  functions. 

Bud  Structure.  A  bud  is  really  an  undeveloped  stem,  with  the 
spaces  between  its  leaves  greatly  shortened,  and  the  leaves  them- 
selves very  small  and  closely  packed.  The  chief  function  of  a  bud 
is  to  keep  the  growing  point  of  the  stem  protected  from  harm 
and  yet  ready  for  rapid  growth  at  the  right  time.  To  carry  out 
this  purpose,  buds  have  several  interesting  adaptations. 

In  the  first  place,  they  are  usually  covered  with  small  leaf- 
like  organs  called  bud-scales,  which  overlap  as  shingles  do,  and 
protect  the  tender  shoot  from  loss  of  water,  mechanical  injury, 
rain,  and  insect  attacks.  Often  the  scales  are  covered  with  a 
sticky  gum,  which  aids  it,  especially  as  regards  the  control  of  water. 

Within  the  bud,  the  tiny  leaves  are  frequently  packed  in  a 
woolly  down,  which  helps  protect  from  injury,  especially  when 
the  bud  is  first  opening,  and  may  also  prevent  ill  effects  from 


STEMS,   THEIR   FORMS   AND    FUNCTIONS  73 

sudden  changes  of  temperature.  The  leaves  themselves  are 
wonderfully  well  packed,  so  as  to  expose  little  surface,  and  econo- 
mize space;  they  may  be  folded,  rolled,  or  coiled,  but  always 
in  the  same  way  in  the  same  plant. 

Buds  are  always  developed  either  at  the  end  of  the  stem 
(terminal),  or  just  above  the  leaves  (lateral).  Their  growth 
consists  of  three  stages,  the  opening  of  the  scales,  the  lengthening 
of  the  stem,  and  the  expansion  of  the  leaves.  The  scales  fall  off 
during  this  process,  leaving  the  bud-scale  scars  to  mark  their 
former  place.  As  most  buds  begin  growth  in  the  spring,  these 
rings  of  scars  mark  the  beginning  of  each  year's  growth.  The 
age  of  the  stem  can  thus  be  calculated  as  long  as  the  scars  show. 

SUMMARY 
Definition. 
Characteristics  of  stem 

Bears  leaves,  flowers,  fruit. 

Leaves  and  branches  at  nodes. 

Growth  between  nodes. 
Functions : 

{of  leaves  for  light  and  air. 
of  flowers  for  pollenation. 
of  fruits  for  dispersal. 

Transportation  of  liquids  between  root  and  leaf 
Storage  of  food. 
Propagation. 

Kinds  of  Branching: 

Object  of  branch  arrangement  in  general. 
Branching  due  to  leaf  arrangement. 

Opposite.     (Ex.) 

Alternate.     (Ex.) 
Branching  due  to  bud  development. 

1.  Excurrent.     (Ex.) 

Shape  of  tree.     Cause. 
Advantages: 

Rapid  growth  in  height. 

Little  storm  resistance. 

Can  grow  closely. 

Shed  snow  readily. 

2.  Deliquescent.     (Ex.) 

Shape  of  tree.     Cause. 
Advantages,  shades  out  its  neighbors. 
Few  can  grow  together. 


74  BIOLOGY  FOR  BEGINNERS 

3.  Forked.     (Ex.) 

4.  Indefinite.     (Ex.) 

Modification  of  Stems: 

1.  Shortened  stems.     (Ex.) 

Advantages,  escape  grazing  animals,  or  crushing. 
Crowd  away  neighbors. 
Retain  water  at  roots. 

2.  Creeping  stems.     (Ex.) 
Advantages,  widespread,  little  wood. 

Escape  injury. 
Propagation. 

3.  Climbing  stems. 

Advantages,  escape  from  shade  conditions. 

Expose  leaves  with  little  wood  tissue. 
Means  of  climbing: 

Twining.     (Ex.)     Method  of  operation. 

Tendrils.     (Ex.)     Method  of  operation. 

Adventitious  roots.     (Ex.) 

Leaf  stalks.     (Ex.) 

4.  Fleshy  stems.     (Ex.) 

Advantages:    Safe  storage,  early  start,  propagation. 
Buds. 

Definition. 

Function. 

Adaptations: 

Scales. 

Gum  or  hairs. 

Woolly  packing. 

Leaf  arrangement. 
Location. 

Manner  of  growth. 
Bud  scale  scars. 

COLLATERAL   READING 

Studies  in  Plant  Life,  Atkinson,  pp.  33-39;  Lessons  with  Plants,  Bailey, 
pp.  1-44;  School  and  Field  Botany,  Gray,  pp.  27-32,  69-70;  Plant  Rela- 
tions, Coulter,  pp.  53-87;  Botany  for  Schools,  Atkinson,  pp.  37-60;  Text- 
book of  Botany,  Gray,  pp.  45-51,  69-85;  Kerner  and  Oliver,  Vol.  I,  Part 
2,  pp.  465-482,  710-736;  Plant  Life  and  Uses,  Coulter,  pp.  143-198; 
Experiments  in  Plants,  Osterhout,  pp.  224-285;  Plants  and  their  Children, 
Dana,  pp.  112-124;  Applied  Biology,  Bigelow,  pp.  163-188;  Structural 
Botany,  Gray,  pp.  50-64,  70-82;  Plant  Structures,  Coulter,  pp.  280-296; 
Lessons  in  Botany,  Atkinson,  pp.  61-68;  Elementary  Studies  in  Botany, 
Coulter,  pp.  224-252. 


CHAPTER  XI 

STEM   STRUCTURE 

Vocabulary 

Lenticels,  openings  in  the  bark  for  passage  of  air  and  water  vapor. 

Radiating,  extending  out  from  the  center. 

Fabric,  woven  material  such  as  cloth. 

Perennial,  living  year  after  year. 

Dicotyledonous,  plants  having  two  cotyledons.     (Dicots.) 

Monocotyledonous,  plants  having  one  cotyledon.     (Monocots.) 

EXTERNAL  STRUCTURE 

The  external  structure  of  all  ordinary  stems,  though  varying 
greatly,  has  some  points  in  common.  It  will  be  seen  that  there  is 
an  outer  covering,  the  epidermis  or  bark,  which  protects  from 
injury  by  storm  and  insects  and  prevents  undue  loss  of  water,  as 
a  result  of  drought  or  cold. 

Lenticels.  Through  this  bark  are  openings  (lenticels)  which 
permit  a  regulated  escape  of  water- vapor,  and  also  admit  air. 

Leaf  Scars.  On  the  bark  will  be  found  scars  left  by  leaves  of 
preceding  seasons,  varying  in  location  according  as  the  leaves 
were  opposite  or  alternate,  and  having  above  them  the  buds  for 
the  coming  year's  branches.  On  these  scars  will  be  found  dots 
marking  the  severed  ends  of  the  ducts,  which  can  be  traced  into 
the  stem  and  found  to  extend  to  the  roots.  Over  these  scars  is  a 
water-proof  coat  (abscission  layer)  which  formed  before  the  leaf 
fell  to  protect  the  plant  against  the  loss  of  so  many  leaves  and 
consequent  bleeding  from  thousands  of  tiny  wounds. 

Flower-bud  and  Fruit  Scars.  It  frequently  happens  that  the 
bearing  of  a  flower  or  fruit  makes  a  scar  differing  from  those  made 

75 


76 


BIOLOCzY   FOR  BEGINNERS 


by  falling  leaves.    These  are  especially  plain  in  the  horse-chestnut. 

A  flower-bud  always  ends  the  growth  of  the  stem  that  bore  it,  hence 

further  growth  is  by  lateral  buds  which  produce  a  forked  type  of 

branching,  where  the  flower  was  borne. 

Bud-scale  Scars.    At  various  places  on  the  stem  are  rings  of 

small  scars  caused  by  the  bud-scales  of  previous  years  which  were 

shed  as  spring  activity 
commenced,  thus  mark- 
ing the  first  growth  of 
each  year.  Other  mark- 
ings are  frequently  met 
with,  caused  by  injuries 
from  weather  or  insects. 
These  the  plant  has  met 
by  thickening  its  bark. 

INTERNAL  STRUCTURE 

On  cutting  across  the 
stem  of  ,  any  common 
tree,  the  general  internal 
structure  will  be  shown, 
in  most  cases,  without 
the  use  of  lenses.  Three 
regions  can  be  dis- 
tinguished easily  —  bark,  wood,  and  pith.  A  closer  inspection 
reveals  a  fourth,  between  bark  and  wood.  This  is  the  cambium, 
a  thin,  light-colored  zone  of  very  juicy  cells,  which  here,  as  in 
the  root,  produces  all  the  other  tissues. 

Wood.  The  wood  will  be  seen  to  be  arranged  in  circles,  "  annual 
rings  "  of  alternately  coarse  and  fine  tissue,  the  ducts,  and  wood 
fibers,  while  radiating  from  the  pith  and  extending  across  these 
rings  are  the  pith  rays  that  connect  pith  and  bark. 

Bark.  The  bark  will  repay  a  closer  scrutiny  with  a  hand 
lens  and  will  be  found  to  consist  of  an  outer  epidermal  layer, 
often  variously  thickened  and  roughened  by  growth;  next,  the 


-*-  or  *  Srtrsy  — 


FIG.  15.     Stem   showing   lenticels  and  diff- 
erent kinds  of  buds  and  scars. 


STEM   STRUCTURE 


77 


"  green  layer  "  (cortex),  and  within  this  the  bast  fibers  and  tubes, 
which  transfer  liquids  downward  and  give  toughness  to  the  bark. 

FIG.  16.  Diagram  of  maple  stem  show- 
ing the  development  of  wood  and  bark 
through  first  and  second  years.  At  the  tip 
is  a  mass  of  living  formative  material 
(shown  unshaded)  from  the  sides  of  which 
arise  protrusions  that  become  leaves.  Also 
arising  from  the  formative  region,  just 
above  the  base  of  the  very  young  leaves, 
are  protrusions  which  develop  into  forma- 
tive regions  like  those  of  the  main  tip, 
and,  as  growing-point,  produce  leaf-bearing 
branches  of  the  main  stem.  In  the  center, 
around  the  axis,  the  formative  material  as 
it  grows  older  becomes  pith  (shown  as 
dotted)  and  this  pith  is  continuous  with 
that  of  the  branches.  The  surface  becomes 
changed  into  a  skin  or  epidermis  (coarse 
shading)  covering  both  stem  and  leaves. 
Parts  of  the  formative  material  between 
the  epidermis  and  the  pith  become  vari- 
ously hardened  into  "bundles  of  fibrous  ma- 
terial; around  the  central  pith  arise  strands 
of  wood  (fine  shading) ;  near  the  epidermis 
arise  corresponding  strands  of  bast  (shown 
by  black)  surrounded  by  more  or  less  pith- 
like  material  which  may  become  green  or 
corky,  called  cortex  (shown  dotted  like  the 
pith);  and  between  the  rings  of  wood  and 
bark  is  a  layer  of  formative  material  which 
is  continuous  with  the  tip  and  is  called  the 
cambium.  From  this  cambium  in  successive 
years  new  wood  is  added  to  that  within 
and  new  bark  to  that  on  its  outer  side,  and 
thus  both  wood  and  bark  increase  in  thick- 
ness by  annual  layers.  But  on  the  outside 
the  epidermis,  and  then  the  older  bark,  is 
pushed  off  or  worn  away  so  that  the  total 
thickness  of  the  bark  is  limited.  Both 
wood  and  bark  are  continued  into  the 
leaves,  but  not  the  cambium.  The  strands 
of  wood  and  those  of  the  bark  are  so  connected  as  to  form  a  sort  of  net- 
work through  the  meshes  of  which  extend  radially  the  plates  of  pith  called 
pith-rays. 

From  Sargent. 


78  BIOLOGY  FOR  BEGINNERS 

FUNCTIONS  OF  STEM  TISSUES 

The  tissues  in  order  from  without  are  the  epidermis,  cortex, 
bast  fibers  (hard  bast),  bast  tubes  (soft  bast),  cambium,  wood, 
ducts,  pith,  and  pith  rays  from  center  to  cortex.  Each  of  these 
layers  has  its  definite  functions,  several  of  which  have  been  stated. 

Epidermis.  The  outer  layer,  or  epidermis,  is  largely  protective 
and  hi  several  ways.  Its  thickness  guards  against  injury  from  wind, 
weather,  and  attacks  of  insects.  It  does  not  allow  loss  of  water, 
except  at  the  lenticels,  thus  preventing  undue  drying  of  the  deli- 
cate tissues  beneath.  It  also  keeps  out  the  spores  of  parasitic  fungi 
that  might  otherwise  find  entrance  and  destroy  the  plant. 

Cortex.  Under  the  epidermis  is  the  cortex,  whose  function  is 
to  help  prepare  starch  food  for  the  plant,  much  as  do  the 
leaves. 

Bast  Fibers.  The  bast  fibers  give  toughness  to  the  bark,  some- 
times helping  support  the  stem.  Man  has  taken  advantage  of 
the  fiber  strength  of  hemp  and  flax  (look  up)  to  make  fabrics. 

Bast  Tubes.  The  soft  bast  conveys  food  prepared  by  leaves 
downward  to  various  places  where  it  is  used  or  stored. 

Cambium.  The  growth  function  of  the  cambium  cannot  be  too 
often  mentioned,  as  from  it,  by  a  complicated  process  of  cell  divi- 
sion, bark  tissues  on  the  outside  and  wood  and  ducts  within  are 
formed. 

Ducts.  The  ducts  transfer  liquids  up  and  air  down  in  the  stem, 
and  add  their  strength  to  the  woody  portions,  whose  fibers  are  the 
chief  support  of  the  stems  of  all  larger  plants.  Together  they  make 
up  the  bulk  of  the  stem  tissue. 

Wood  Fibers.  Both  the  wood  fibers  and  ducts  are  arranged  in 
very  definite  circles,  called  annual  rings  because  usually  each  ring 
marks  a  year's  growth.  These  rings  are  caused  by  the  cambium 
which  produces  larger  ducts  and  more  of  them  in  the  spring  when 
the  sap  is  flowing  than  later,  when  more  wood  fiber  is  produced. 
In  the  winter,  the  growth  practically  stops,  only  to  begin  the  fol- 
lowing spring  with  a  layer  of  large  ducts  again,  thus  marking,  by 
these  successive  rings  of  tissue,  the  seasons'  changes. 


STEM   STRUCTURE  79 

Pith.  The  pith  may  be  a  minute  remnant  of  the  formative  tis- 
sue, or  a  larger  storage  place  for  foods  and  the  pith  rays  serve  as 
cross  channel  for  liquids  to  follow  in  their  circulation  in  the  stem. 

So  we  have  one  protective  region,  the  epidermis;  one  digestive 
region,  the  cortex;  one  formative  region,  the  cambium;  one  storage 
region,  the  pith.  The  ducts,  soft  bast,  and  pith  rays  are  the  chan- 
nels for  circulation  of  fluids  while  the  wood  and  bast  fibers  are  for 
strength  and  support. 

Grafting.  The  remarkable  ability  of  the  cambium  cells  to  grow 
and  produce  new  tissues  is  utilized  in  grafting.  Grafting  consists 
in  bringing  into  close  contact  the  cambium  layer  of  a  small  active 
twig  with  that  of  the  tree  upon  which  it  is  to  grow.  This  may  be 
done  by  splitting  the  stem,  and  inserting  the  fresh-cut  twig,  or  by 
raising  the  bark  and  inserting  an  active  budded  twig  beneath  it, 
with  the  cambium  layers  in  contact.  The  wound  is  then  protected 
by  wax  and  growth  between  the  two  cambium  layers  soon  unites 
the  new  stem  with  the  old. 

The  cambium  also  provides  for  the  healing  of  injuries  and  the 
covering  of  scars  where  branches  are  cut  off.  New  tissue  forms  at 
the  edges  of  the  wound  and  gradually  covers  the  whole  area,  pro- 
vided that  spores  and  bacteria  do  not  first  cause  decay  of  the  ex- 
posed surface.  To  prevent  this,  cut  or  injured  surfaces  should  al- 
ways be  tarred  or  painted  to  kill  and  keep  out  bacteria,  while  new 
tissue  is  growing.  If  decay  has  begun  the  rotted  wood  must  be 
cleanly  removed,  the  cavity  sterilized  with  tar  and  filled  with 
cement.  The  cambium  growth  will  now  extend  the  tissue  inward 
from  the  edges  and  often  cover  the  scar,  filling  and  all.  , 

In  rare  instances  two  limbs,  or  even  two  separate  trees  of  the 
same  kind,  will  chafe  together  in  the  wind,  till  the  cambium  is 
exposed  in  both.  Then  if  undisturbed,  an  automatic  graft  may 
occur  and  a  curious  condition  will  develop,  in  which  the  two  trees 
will  continue  to  grow  firmly  together. 

Other  Kinds  of  Stem  Structure.  In  the  chapter  on  seed  struc- 
ture it  was  stated  that  plants  whose  seeds  had  two  cotyledons 
(dicotyledonous  plants)  had  stems  that  differed  from  plants  whose 
seeds  had  one  cotyledon  (monocotyledonous) .  The  stem  just 


80 


BIOLOGY  FOR  BEGINNERS 


described  is  such  a  one  as  would  be  found  in  a  dicotyledonous 
plant.    The  monocotyledonous  stem  differs  in  so  many  ways  that 

it  requires  special  consideration. 
Corn  Stems.  The  common 
corn  stalk  is  a  good  example  of 
the  monocotyledonous  type  of 
stem.  If  we  cut  a  section  across 
it,  we  find  the  tissues  very  dif- 
ferently arranged  from  those  in 
the  dicotyledonous  stem,  just 
discussed.  The  monocotyledon, 
in  place  of  a  bark  of  several  lay- 
ers, has  a  rind  of  only  one  kind  of 
tissue  —  thick- walled,  hard  cells 
whose  function  is  mainly  to  sup- 
port the  plant.  The  wood, 
cambium,  and  bast  tissues  are 
grouped  in  numerous  "vascular 
bundles"  which,  instead  of  being 
in  definite  rings,  are  scattered 
through  the  stem,  the  larger  and 
older  ones  toward  the  center  and 
smaller  and  younger  ones  near 
the  edge.  The  cambium  in  mono- 
cotyledons ceases  to  build  new 
tissue,  after  a  time.  Hence  the 
stem  does  not  continue  to  in- 
crease in  diameter  as  does  the 
dicotyledonous  stem,  but  pro- 
duces tall  slender  plants  like  corn, 
grasses,  bamboos,  and  palm  trees. 
The  bulk  of  the  stem  consists  of 
the  soft  thin-walled  pith,  instead 
of  wood  and  ducts,  so  that  the 


FIG.  17.    Diagram  of  palm  stem 
(monocot).    From  Sargent. 


structure  is  almost  reversed  in  these  two  types  of  stems  although 
the  same  tissues  are  present.    As  one  result  of  this  striking  dif- 


STEM  STRUCTURE 


81 


ference  we  obtain  many  of  our  wood  products  from  the  dicoty- 
ledonous stems,  while  the  monocotyledonous,  having  little  wood 
and  much  pith  for  storage,  provide  us  with  foods  such  as  hay 
and  grain,  sugar-cane,  and  starch. 

Do  not  think  that  the  monocotyledonous  stem  is  weak  because 
it  has  so  little  wood  tissue  —  the  case  is  quite  the  contrary  as  you 
may  prove  for  yourself. 
Select  a  tall  grass  stem, 
such  as  timothy  or  rye. 
Measure  its  height  and  its 
diameter.  How  many 
times  its  thickness  is  the 
height?  Suppose  it  were  a 
tree  one  foot  in  diameter 
how  tall  would  it  be?  Com- 
pare this  with  the  actual 
height  of  trees.  Figure 
this  out  and  you  will 


jttHacorvi.C.DO/1  o us    Trff  . 


FIG.  18.    Cross  section  of  typical 
monocotyledonous  stem. 


have  more  respect  for  the 

strength  of  the  grass  stem,  as  well  as  for  the  "  sturdy  oak." 

Polycotyledonous  Stems.  Seeds  having  several  cotyledons 
(polycotyledonous)  have  a  woody  stem  with  annual  rings,  but 
differing  in  other  ways  from  'the  two  preceding  types.  We  shall 
not  take  up  its  structure  in  detail;  pines,  spruces  and  all  ever- 
green trees  belong  to  this  last  group  and  their  resinous  wood 
furnishes  us  with  our  best  lumber. 

Not  only  are  their  stems  of  great  strength,  but  some  of  them 
are  the  largest  and  oldest  living  things  in  the  world.  The  Big 
Trees  (Sequoia)  of  California  are  the  oldest,  even  among  trees. 
One  of  these  ancient  giants,  the  "  General  Sherman  Tree,"  is  nearly 
four  thousand  years  old,  279  feet  high,  and  36  feet  in  diameter. 

To  put  it  another  way,  it  was  a  flourishing  sapling,  twenty  or 
thirty  feet  high  when  the  Exodus  of  Israel  and  the  Trojan  wars 
took  place.  It  was  a  thousand  years  old  at  the  time  of  Solomon 
and  two  thousand  at  the  birth  of  Christ.  All  our  European  and 
American  history  are  but  events  of  yesterday  to  this  patriarch  of 


82 


BIOLOGY  FOR  BEGINNERS 


FIG.  19.     Sequoia  Washingtoniana  (Bureau  Forestry,  U.  S.  Dept.  Agr.) 
From  Atkinson. 


STEM   STRUCTURE 


83 


the  organic  world,  which  now  towers  higher  than  a  twenty-story 
building  and  is  still  growing.  Some  animals,  such  as  the  elephant, 
may  live  two  hundred  years,  but  even  these,  or  man,  with  his  three 


Courtesy  of  the  American  Museum  of  Natural  History. 

FIG.    20.    Section  of  one  of  the  big  trees  of  California,  the  "  Mark  Twain," 
16  ft.  in  diameter,  and  1341  years  old. 

score  years  and  ten,  are  the  merest  infants  beside  such  ancient 
inhabitants  of  the  vegetable  world. 

This  illustrates  a  fact  which  is  often  overlooked,  that  perennial 
plants  really  have  no  limit  of  growth,  as  do  animals,  but  keep  on 


84 


BIOLOGY    FOR  BEGINNERS 

STEM  STRUCTURE 


External  Features 

Structure 

Function 

Bark 

Protection 

Lenticels 

Spongy  openings 

Let  out  water  vapor 

Admit  air 

Scars  left  by 

• 

1.  Leaves  showing 

Duct  scars 

Cut  ends  of  ducts 

Abscission  layer 

Water  proof  cover 

Prevent  loss  of  sap 

2.   Bud  scales 

Formed  in  spring 

Mark  year's  growl  h 

3.   Flowers  and  fruit 

Usually  terminal 

Cause  branch  to  fork 

Internal  Features 


1.   Bark 

Epidermis 

Thin  if  young,  corky  in 

Protect    from     insects, 

older  stems 

fungi  and  weather 

Retain  water 

Cortex 

Thin  walled,  soft  cells 

Food    making  and   di- 

gestion 

Bast  fibers 

Thick  and  tough 

Strength 

Bast  tubes 

Long,  tubular  cells 

Downward  transfer 

2.  Cambium 

Very     active,     proto- 

Growth 

plasm 

3.  Wood  region 

Wood  fibers 

Thick  walled,  stiff 

Support 

Ducts 

Thick  walled,  tubular 

Upward  transfer 

4.  Pith 

Thin  walled,  weak 

Storage 

Pith  rays 

Cross  transfer 

Comparison  of  Dicot  and  Monocot  Stems 


Features  of  each 

Dicot 

Monocot 

Outer  layer 

Bark  of  several  tissues 

Rind  of  one  tissue 

Vascular  bundles 

In  regular  rings 

Scattered 

Bulk  of  stem 

Wood 

Pith 

Supported  by 

Wood  region 

Rind 

Cambium 

Permanent 

Not  permanent 

Growth 

Continuous  in   height 

In  height  only 

and  thickness 

Use 

For  lumber,  fuel,  etc. 

For  food  stored 

Usual  shape 

Thick 

Tall,  slender 

Examples 

Broad-leaved  trees  and 

Grasses,    lilies,    palms, 

common  plants 

sugar-cane,  etc. 

STEM    STRUCTURE  85 

increasing  slowly  in  size  for  indefinite  periods,  while  animals  reach 
a  maximum  size  and  grow  no  larger,  no  matter  how  old  they  become. 
The  reason  is  probably  that  in  plants,  little  energy  is  required, 
hence  little  food  is  used  in  oxidation  and  more  is  left  for  additional 
growth,  whereas  in  animals,  which  use  more  energy,  a  point  is 
reached,  where  the  nutritive  processes  are  just  balanced  by  oxida- 
tion and  further  growth  ceases.  As  soon  as  the  destructive  proc- 
esses exceed  the  constructive,  old  age  enters  and  finally  death 
itself. 

COLLATERAL   READING 

Science  of  Plant  Life,  Transeau,  pp.  118-136;  Botany  of  Crop  Plants, 
Robbins,  pp.  33-41;  Fundamentals  of  Botany,  Gager,  pp.  61-68;  Plant 
Anatomy,  Stevens,  pp.  28-60;  Principles  of  Botany,  Bergen  and  Davis, 
pp.  57-79;  Botany  for  Schools,  Atkinson,  pp.  51-60;  Introduction  to  Botany, 
Stevens,  pp.  45-64;  Plant  Life  and  Plant  Uses,  Coulter,  pp.  162-185;  Plant 
Structures,  Coulter,  pp.  232-237;  Elementary  Botany,  Coulter,  pp.  224-252; 
Applied  Biology,  Bigelow,  pp.  163-188;  Elementary  Biology,  Peabody  and 
Hunt,  pp.  45-52;  Biology,  Coleman  and  Bailey,  pp.  59-72;  Plant  Relations, 
Coulter,  pp.  83-87. 


CHAPTER  XII 

LEAVES  AND  LEAF   STRUCTURE 

Vocabulary 

Surplus,  an  extra  supply. 

Originate,  to  begin. 

Accumulated,  collected  together. 

Excessive,  too  great. 

Communicate,  to  connect. 

Stomates,  openings  in  leaf  epidermis  to  admit  air  and  let  out  water 

vapor. 

Heliotropism,  the  response  of  plant  parts  to  light. 
Chlorophyll,  the  green  coloring  matter  of  plants. 
Transpiration,  the  passing  off  of  excess  water  from  plants. 
Vascular,  composed  of  "vessels"  or  tubular  cells,  such  as  the 

vascular  bundles  of  ducts  in  stem  and  leaf. 
Parenchyma,  thin-walled,  spongy  plant  tissue. 

Leaf  Functions.  The  leaf  is  one  of  the  most  remarkable  and 
important  parts  of  the  plant.  Within  it  are  performed  more  life 
functions  than  in  any  other  plant  or  animal  organ.  Its  chief  and 
unique  function  is  the  manufacture  of  starch  out  of  water  from  the 
soil  and  carbon  dioxide  from  the  air.  Animals  cannot  prepare 
starch  from  these  two  compounds  and  must  therefore  depend 
upon  plants  for  their  supply.  Not  only  does  it  prepare,  but  it 
also  digests  and  assimilates  food,  sending  its  surplus,  by  way 
of  the  veins  (duct  bundles),  to  all  living  parts  of  the  plant. 
Furthermore,  the  leaves  are  constructed  so  as  to  admit  air  for 
oxidation,  and  to  throw  off  carbon  dioxide  (respiration).  Ex- 
cretion of  water  (transpiration)  and  of  other  wastes  is  another 
function  of  these  versatile  organs.  They  also  possess  in  some 
degree  the  powers  of  motion  and  reproduction.  Food  making, 
digestion,  assimilation,  respiration,  excretion,  motion,  reproduction, 
—  these  are  all  the  functions  that  any  living  thing  can  perform. 
One  entirely,  and  all  to  some  extent,  are  performed  in  the  leaf. 

86 


LEAVES  AND  LEAF  STRUCTURE 


87 


GENERAL  STRUCTURE  OF  LEAVES 

A  leaf  usually  consists  of  a  thin  flattened  portion  (the  blade) 
stiffened  by  a  framework  of  veins  which  are  really  bundles  of 
ducts  connecting  with  those  in  the  stem.  Usually  the  blade  is 
attached  to  the  stem  and  held  out  into  the  light  by  a  stalk  (the 
petiole).  Its  point  of  at- 
tachment is  called  the 
node  of  the  stem,  above 
which  all  branch  buds 
originate.  The  veins  may 
form  a  network  throughout 
the  leaf  or  may  be  almost 
parallel  (grass).  There 
may  be  one  large  midvein 
with  branches  like  a  feather 
(elm),  or  several  veins  of 
equal  size  may  spread  from 
the  petiole  like  the  fingers 
of  your  hand  (maple), 
but  whatever  the  arrange- 
ment, their  function  is 
to  support  the  blade  and 
transfer  the  liquids  concerned  in  the  various  leaf  processes. 

Leaf  Forms.  The  outline  of  a  leaf  depends  largely  upon  the 
arrangement  of  its  veins.  If  netted  veined  the  leaves  are  usually 
broad,  notched,  or  lobed;  while  if  the  veins  are  parallel  they  are 
usually  long  and  slender.  The  forms  of  the  leaves  are  almost  as 
various  as  the  kinds  of  plants;  some  having  regular  or  entire  edges 
(lily),  others  notched,  lobed,  or  finely  divided  (elm,  maple,  carrot), 
while  still  others  are  composed  of  separate  leaflets  (pea,  horse 
chestnut),  and  so  are  called  compound. 

ADAPTATIONS  FOR  EXPOSURE 

Form.  These  different-shaped  leaves  are  developed  with  but 
one  end  in  view —  the  complete  exposure  of  the  leaf  tissues  to 


FIG.  21.    Structure  of  leaf  —  exterior. 


88 


BIOLOGY  FOR  BEGINNERS 


light  and  air,  on  both  of  which  all  the  activities  of  the  leaf 
depend. 

Arrangement.  Not  only  are  leaves  adapted  by  their  shape  for 
this  exposure,  but  by  their  arrangement  on  the  stem.  Look  at  a 
tree  from  above  or  at  a  house  plant  from  the  "  window  side  "  and 
observe  that  the  branches  and  leaf  stems  (petioles)  have  so  ex- 
tended and  twisted  them- 
selves, that  each  leaf  is 
exposed  and  very  few  cast 
any  shade  upon  their 
neighbors. 

Heliotropism.  Another 
adaptation  for  leaf  ex- 
posure is  their  ability  to 
constantly  turn  them- 
selves toward  the  light. 
This  is  an  every  day 
observation,  but  no  one 
can  explain  just  how  they 
do  it.  The  process  is  called 
heliotropism  (which  means 
sun  turning),  and  is  very 
essential  to  the  work  of 

the  leaves.  Roots  turn  from  light  (negative  heliotropism)  while 
this  response  made  by  leaves  toward  the  light  is  termed  positive 
heliotropism. 

Modified  Leaves.  Like  roots,  leaves  are  often  modified  to 
perform  special  functions:  They  may  be  reduced  to  mere  ten- 
drils for  climbing  (pea)  or  they  may  develop  as  thorns  for  protec- 
tion (barberry).  They  may  thicken  up  with  stored  nourishment 
and  even  reproduce  the  plant  (live-f or-e ver) ,  or  most  curious  of 
all,  may  develop  into  traps  for  insects  (sundew  and  pitcher-plant) . 
Fall  of  Leaves.  Most  plants  of  temperate  climates  shed  their 
leaves,  either  all  at  once  in  autumn  (maples,  elms)  or  a  few  at  a 
time  the  year  round  (pines  and  spruces).  They  do  this  so  they 
may  rid  themselves  of  waste  mineral  matter  that  has  accumulated 


FIG.  22.     Sunflower  with  young  head  turned 
to  the  morning  sun.     From  Atkinson. 


LEAVES  AND  LEAF  STRUCTURE 


89 


and,  in  the  case  of  the  broad-leaved  plants,  this  shedding  also  comes 
because  it  is  necessary  to  reduce  the  exposed  surface  so  that  too 
much  water  may  not  be  evaporated  in  the  winter,  when  the  roots 
can  supply  but  little.  Of  course  one  can  see  another  reason  for 
plants  that  grow  in  climates  where  snow  prevails  during  the  winter. 
The  weight  of  snow  accumulated  by  the  leaves  would  tend  to 

break   the  plant   down. 

In  the  case  of  the  pines 
with  their  slender 
needles  this  reason  does 
not  apply. 

The  color  changes  of 
autumn  are  not  due  to 
frost  entirely,  but  may 
be  caused  by  anything 
which  stops  the  activity 
of  the  plant.  The 
beautiful  yellows  and 
reds  that  make  our 
autumn  a  blaze  of  glory 
act  as  a  protection  to  the 
sensitive  green  sub- 
stance of  the  leaves, 
which  is  being  withdrawn  and  stored  for  use  another  year. 

Before  the  leaves  of  a  plant  fall  there  is  formed  at  each  leaf 
base  a  waterproof  layer  (abscission  layer)  which  prevents  the  loss 
of  sap  after  the  leaf  is  gone. 

The  enormous  amount  of  ashes  left  when  the  leaves  are  burned 
gives  some  idea  of  the  amount  of  unused  mineral  matter  which 
the  plant  had  stored  there,  and  incidentally  reminds  us  that  plant 
ashes,  whether  from  stems  or  leaves,  are  useful  food  materials  for 
plants  and  ought  to  be  put  back  on  the  soil  for  use  another  year. 

MINUTE  STRUCTURE  OF  LEAVES 

The  chief  function  of  the  leaf  is  the  manufacture  of  food  ma- 
terials. To  understand  this,  a  thorough  study  of  the  minute 
structure  is  necessary. 


FIG.  23.  The  same  plant  at  sundown 
showing  the  head  turned  to  the  west.  From 
Atkinson. 


90  BIOLOGY  FOR  BEGINNERS 

If  the  blade  of  a  leaf  be  cut  across  and  studied  with  a  micro- 
scope, the  following  tissues  may  be  observed.  Mentioned  in  order 
from  the  upper  surface  they  are: 

1.  The  cuticle  (sometimes  lacking). 

2.  The  upper  epidermis. 

3.  The  palisade  cells. 

4.  The  spongy  layer  (traversed  by  veins). 

5.  The  air  spaces. 

6.  The  lower  epidermis  (penetrated  by  stomates). 

The  Upper  Epidermis.  This  usually  consists  of  a  single  layer 
of  cells  often  very  irregular,  as  seen  from  above,  but  brick  shaped 
when  viewed  in  cross  section.  There  are  few  stomates  in  the 
upper  epidermis,  since  they  would  be  exposed  to  dust  and  rain. 
The  function  of  the  upper  epidermis  is  to  prevent  loss  of  water. 
To  aid  in  this,  it  is  sometimes  covered  by  a  waxy  layer,  called 
the  cuticle,  as  in  ivy,  cabbage,  and  other  leaves  that  shed  water 
in  drops.  A  second  function  of  these  epidermal  cells  may  be  to 
act  as  lenses  and  concentrate  the  sunlight  upon  the  inner  parts 
of  the  leaf.  The  fact  that  their  upper  and  lower  surfaces  are 
curved  like  a  lens,  leads  to  this  supposition. 

The  Palisade  Layer.  Next  beneath  the  upper  epidermis  is  the 
palisade  layer.  It  consists  of  long  narrow  cells,  placed  endwise, 
at  right  angles  to  the  surface  of  the  leaf.  Within  these  cells  is 
found  the  chlorophyll,  which  is  the  green  coloring  matter  of  all 
plants.  As  you  will  learn  later,  it  is  very  sensitive  to  light  and 
these  long  cells  permit  the  chlorophyll  grains  to  move  to  the  upper 
ends  if  the  light  be  dim,  or  to  retreat  to  the  long  side  walls  if  the 
light  is  too  strong. 

The  function  of  the  palisade  layer,  then,  is  to  regulate  the  ex- 
posure of  chlorophyll  to  light,  and  to  carry  on  starch  making. 

The  Spongy  Layer.  Beneath  the  palisade  layer  is  a  spongy 
layer  which  consists  of  thin-walled  cells  and  air  spaces,  and  is 
penetrated  in  all  directions  by  veins  (duct  bundles).  The  spongy 
cells  are  roundish,  irregular,  and  loosely  packed,  thin  walled,  and 
full  of  protoplasm  and  chlorophyll.  In  them,  as  in  the  palisade 


LEAVES  AND  LEAF  STRUCTURE         91 

layer,  starch  making  and  all  the  other  leaf  functions  are  carried 
on.  The  passing  off  of  water  to  the  air  spaces  is  part  of  its  work. 
The  air  spaces  are  usually  large,  irregular  cavities  among  the 
spongy  cells.  They  open  through  the  lower  epidermis  by  way  of 
the  stomates,  their  function  being  to  receive  water  vapor  from  the 
spongy  cells  and  to  pass  it  out  through  these  openings.  They 
also  permit  oxygen  and  carbon  dioxide  to  pass  to  all  the  cells  of  the 
spongy  layer.  They  are  very  important,  since  through  them  food 
making,  respiration,  and  transpiration  go  on.  They  occupy  about 
three-fourths  of  the  bulk  of  the  spongy  layer.  The  veins  or  duct 
bundles  are  scattered  through  the  spongy  layer  transporting  water 
and  food  stuffs  and  supporting  the  blade  of  the  leaf. 

The  Lower  Epidermis.  Like  the  upper,  the  lower  epidermis 
usually  has  but  one  layer  of  cells.  Through  it  open  many  stomates 
which  regulate  the  passage  of  air  and  water  vapor  to  and  from  the 
inside  of  the  leaf. 

The  Stomates.  These  have  been  referred  to  as  openings  through 
the  epidermis.  They  are  minute  slit-like  holes,  about  one-twen- 
tieth as  wide  as  the  thickness  of  this  paper.  On  each  side  of  the 
slit  is  an  oval  guard  cell  which  regulates  the  opening  and  closing 
of  the  stomate.  Controlled  by  the  needs  of  the  plant,  the  sto- 
mates open  when  there  is  an  excess  of  water  to  be  passed  off,  and 
close  in  a  drought.  They  open  when  carbon  dioxide  is  required 
for  starch  making  or  air  for  breathing,  and  close  when  either  process 
stops,  thus  regulating,  in  a  remarkable  degree,  the  activities  of  the 
leaf.  The  function  of  the  stomates  is  threefold, 

1.  To  admit  carbon  dioxide  for  starch  making. 

2.  To  regulate  transpiration  of  water  vapor. 

3.  To  admit  oxygen  and  liberate  carbon  dioxide  in  respiration. 
However,  this  elaborate  mechanism  would  be  of  little  use  were 

it  not  for  the  extensive  system  of  air  spaces  in  the  spongy  tissue  of 
the  leaf  into  which  the  stomates  open,  and  by  means  of  which  all 
parts  may  have  access  to  air  for  starch  making,  respiration,  and 
transpiration.  Their  number  may  vary  from  60,000  to  450,000 
per  square  inch  and  is  usually  greatest  on  the  lower  surface  where 
they  are  best  protected  from  dust  and  rain.  Floating  leaves  have 


92 


BIOLOGY   FOR   BEGINNERS 


all  their  stomates  on  the  upper  surface.     In  vertical  leaves  they 
are  evenly  distributed. 

Chlorophyll.    The  green  coloring  matter  of  plants  is  the  most 
important  part  of  the  leaf.    Practically  the  whole  function  of  the 


CROSS 


FIG.  24.    Leaf  Structure. 

rest  of  the  leaf  is  to  expose  the  chlorophyll  to  light  and  provide 
it  with  materials  upon  which  to  work.  Chlorophyll  is  composed 
of  nearly  all  the  elements  we  find  in  any  plant  tissue,  but  is  espe- 
cially rich  in  iron  compounds  which  give  it  its  green  color.  It  is 


LEAVES  AND  LEAF  STRUCTURE         93 

found  in  the  form  of  very  minute  particles  called  chlorophyll 
grains,  or  chloroplasts,  which  seem  to  consist  of  active  protoplasm 
combined  with  the  green  chlorophyll.  This  is  the  substance  which 
performs  the  essential  function  of  the  leaves.  It  is  found  mainly 
in  the  palisade  cells  and  spongy  layer.  The  former  are  arranged 
to  regulate  its  exposure  to  light,  and  the  latter  to  provide  it  with 
carbon  dioxide  and  water  to  use  in  starch  making.  We  shaU  devote 
the  next  chapter  to  the  way  in  which  it  does  its  work.  For  the 
present,  think  of  chlorophyll  as  occurring  in  the  form  of  active, 
green  grains,  found  in  all  green  parts  of  plants  and  very  essential 
to  their  growth. 

SUMMARY 
Functions : 

1.  Starch  making. 

2.  Digestion  and  assimilation. 

3.  Respiration. 

4.  Excretion. 

5.  Reproduction. 

General  structure: 

1.  Blade. 

2.  Petiole  (leaf  stalk)  attached  at  nodes. 

3.  Veins  (duct  bundles). 

Functions,  support  and  transportation. 
Arrangement : 
Parallel  (grasses). 
Netted: 

Feather  veined  (elm). 
Finger  veined  (maple). 

4.  Outline. 

Irregular  margin  in  netted  veined  leaves. 
Regular  margin  in  parallel  veined  leaves. 

•Adaptation  for  exposure  to  light  and  air: 

1.  Shape,  so  as  to  let  light  through  to  others. 

2.  Arrangement,  opposite  or  alternate. 

3.  Heliotropism. 

Positive  in  leaves  and  flowers. 
Negative  in  roots. 

Modified  leaves,  as 

1.  Tendrils,  for  climbing  (pea). 

2.  Thorns  for  protection  (barberry). 

3.  Thickened,  for  storage  (cactus). 

4.  Traps,  for  catching  insects  (sun-dew). 


94  BIOLOGY   FOR  BEGINNERS 

Fall  of  Leaves: 

1.  Reasons. 

Remove  waste  mineral  salts. 
Lessen  exposure  to  storms. 
Reduce  surface  for  transpiration. 

2.  Cause  of  coloration.     Function. 

3.  Abscission  layer. 

SUMMARY  OF  MINUTE  STRUCTURE  OF  LEAVES 

1.  Upper  Epidermis. 

Structure:  One  layer,  brick-shaped  cells,  few  stomates. 

Cuticle  sometimes  present. 
Function:  Prevent  loss  of  water. 

Concentrates  sunlight  on  chlorophyll. 

2.  Palisade  Layer. 

Structure:    Narrow,  perpendicular  cells.     Contain  chlorophyll. 
Function:    Regulate  exposure  of  chlorophyll. 

3.  Spongy  Layer. 

(a)  Spongy  cells. 

Structure:   Thin,  irregular,  loose,  active. 

Function:   Starch  making  and  transpiration. 
(6)  Air  spaces. 

Structure :  Large  irregular  cavities. 

Function:   Transpiration,  air  supply. 
(c)  Veins. 

Structure:   Bundles  of  ducts  and  wood  fibers. 

Function:  Transportation  and  support. 

4.  Lower  Epidermis. 

Structure:   Single  layer  of  cells,  many  stomates. 

Function:   Regulation  of  water  and  air  supply  via  stomates. 

5.  Stomates. 

Structure:  Slit-like  opening  and  guard  cells. 

Function:    Regulate  transpiration,  supply  of  carbon  dioxide  and  of 

oxygen. 
Distribution:    Lower  epidermis  usually  very  numerous. 

6.  Chlorophyll. 

Structure:   Active  green  grains,  rich  in  iron  compounds. 
Function:   Photosynthesis  or  starch  making. 
Distribution:   Palisade  cells  and  spongy  layer. 

COLLATERAL   READING 

General  study:  Elementary  Studies  in  Botany,  Coulter,  pp.  187-223; 
Plant  Life  and  its  Uses,  Coulter,  pp.  201-218,  234-255;  Experiments  in 
Plants,  Osterhout,  pp.  163-223;  Familiar  Trees,  Mathews,  pp.  1-19; 
Plants  and  Their  Children,  Dana,  pp.  135-185;  Plant  Relations,  Coulter,  pp. 
6-52;  Botany  for  Schools,  Atkinson,  pp.  70-89;  Flowers,  Fruits  and  Leaves, 


LEAVES  AND  LEAF  STRUCTURE 


95 


Lubbock,  pp.  97-147;  Textbook  of  Botany,  Stevens,  pp.  85-98;  Elementary 
Botany,  Atkinson,  pp.  36-38;  Lessons  in  Botany,  Atkinson,  pp.  56-59; 
Plant  Structures,  Coulter,  pp.  141-142;  Nature  and  Work  of  Plants,  pp. 
80-86;  The  World's  Great  Farm,  Gaye,  Chap.  XII. 

HELIOTROPISM 

How  Plants  Grow,  Bailey,  pp.  350-000;  Lessons  with  Plants,  Bailey, 
pp.  330-000;  Lessons  in  Botany,  Atkinson,  pp.  109-114;  Elementary 
Botany  Atkinson,  pp.  84-88;  Plant  Structures,  Coulter,  pp.  305-000; 
Plant  Relations,  Coulter,  pp.  8-13,  68-70,  138-141,  330-000;  Textbook  of 
Botany,  Strasburger,  pp.  250-253;  Textbook  of  Botany,  Gray  and  Godale, 
pp.  392-393;  Textbook  of  Botany,  Bessey,  pp.  193-194;  Textbook  of  Botany, 
Stevens,  pp.  120-122;  Nature  and  Work  of  Plants,  pp.  73-00. 

STOMATA 

Plant  Physiology,  McDougal,  pp.  196-203;  Plant  Anatomy,  Stevens, 
pp.  127-133;  Lessons  in  Botany,  Atkinson,  pp.  58-59;  Elementary  Botany, 
Atkinson,  pp.  42-44,  46;  Plant  Structures,  Coulter,  pp.  141-143;  Plant 
Relations,  Coulter,  pp.  38-39;  Nature  and  Work  of  Plants,  McDougal, 
pp.  84-00. 

LEAF  ARRANGEMENT 

Flowers,  Fruits  and  Leaves,  Lubbock,  pp.  97-147;  Introduction  to  Botany, 
Stevens,  pp.  81-84;  Plant  Relations,  Coulter,  pp.  6-27;  Kerner"  and 
Oliver,  Vol.  I,  Part  2,  pp.  593-597  and  623-640;  Nature  and  Work  of 
Plants,  McDougal,  pp.  72-75;  Textbook  of  Botany,  Strasburger,  pp.  37- 
40;  Textbook  of  Botany,  Bessey,  pp.  149-150. 

MINUTE  STRUCTURE 


Parts 

Structure 

Function 

Epidermis      (upper 

One  layer;  irregular  cells 

Prevents  loss  of  water 

and  lower) 

Stomates 

Slit  opening  and  guard  cells; 

Regulation  of  excretion 

open  into  air  spaces 

Admit  oxygen  and  CO2 

Palisade  cells 

Oblong,  endwise  to  surface 

Expose    chlorophyll    to 

Have  chlorophyll  grains 

light 

Chlorophyll 

Green,   living  grains  in   the 

Make  starch 

protoplasm 

Spongy  cells 

Irregular,  loose 

All  leaf  functions 

Have  chlorophyll  grains 

Air  spaces 

Large  and  irregular 

Excretion 

Connect  with  stomates 

Respiration 

"Veins" 

Duct  bundles  extending  from 

Support 

the  stem 

Transportation 

CHAPTER  XIII 

LEAF  FUNCTIONS 

Vocabulary 

Illumination,  source  and  supply  of  light. 

Liberated,  set  free. 

Photosynthesis,  the  process  of  starch  formation  in  leaves,  uniting 

carbon  dioxide  and  water  by  means  of  light. 
Soluble,  that  which  can  be  dissolved. 

Photosynthesis.  The  process,  by  which  carbon  dioxide  from 
the  air  and  water  from  the  soil  are  united  by  the  leaves  of  plants 
to  form  starch  through  the  action  of  sunlight  on  the  green  coloring 
matter  in  the  leaves,  is  called  photosynthesis  (meaning  combina- 
tion by  light). 

The  ability  of  plants  to  take  these  two  non-living  substances 
and  build  up  their  own  food  from  them  makes  the  chief  destinc- 
tion  between  plants  and  animals,  for  the  latter  depend  on  plant 
foods  either  directly  or  indirectly.  They  cannot  use  the  raw  ma- 
terials as  do  the  plants. 

Chlorophyll.  The  essential  feature  of  the  leaf,  so  far  as  pho- 
tosynthesis is  concerned  is  the  green  coloring  matter,  chlorophyll 
(leaf  green).  This,  as  described  in  Chapter  XII,  is  found  in  the 
palisade  cells  and  spongy  parenchyma,  in  the  form  of  minute  grains, 
embedded  in  the  protoplasm. 

Chlorophyll  has  the  very  wonderful  property  of  absorbing  some 
of  the  energy  of  the  sun's  light  and  by  the  utilization  of  this  energy 
it  is  able  to  combine  carbon  dioxide  and  water  into  starch.  This 
starch  is  the  primary  form  of  plant  food.  At  the  same  time  that 
starch  is  made,  oxygen  is  thrown  off  as  a  waste  product.  This 
replaces  in  the  atmosphere,  that  which  is  used  in  respiration  by 
animals.  Therefore  animals  depend  on  photosynthesis  for  both 
food  and  oxygen  supply.  It  is  evident  now  why  so  many  adapta- 

96 


LEAF  FUNCTIONS 


97 


tions  are  found  for  exposing  leaves  to  light,  since,  without  light, 
starch-making  cannot  go  on,  and  without  starch  the  plant  cannot 
survive.  The  chlorophyll  is  placed  in  the  long  palisade  cells  so 
that,  if  the  light  be  weak,  the  chlorophyll  bodies  may  move  to  the 
upper  ends  of  the  cells  and  get  better  illumination;  or  if  the  light 
is  too  bright,  they  line  up  along  the  sides  and  so  escape  the  direct 
rays.  In  the  deeper  tissue  of  the  spongy  parenchyma  of  the  leaf, 


Light 


Courtesy  of  American  Museum  of  Natural  History 

FIG.  25.    Activities  going  on  in  the  "cells"  and. air  spaces  of  a  leaf. 

the  chlorophyll  is  sufficiently  protected  and  does  not  need  to  move 
in  this  way;  here  we  find  the  cells  irregular  in  shape. 

Materials  used  in  Photosynthesis.  The  water  for  starch  mak- 
ing is  supplied  from  the  soil  by  means  of  the  absorption  of  the 
roots.  It  rises  to  the  leaves  by  way  of  the  ducts  and  veins.  Any 
excess  is  disposed  of  through  the  stomata.  The  carbon  dioxide 
is  supplied  from  the  air,  where  oxidation,  respiration,  combustion, 
fermentation,  and  decay  are  constantly  producing  it.  As  fast  as 
the  plants  remove  it  they  return  the  oxygen.  As  a  result  the 
composition  of  the  air  remains  practically  constant. 


BIOLOGY  FOR  BEGINNERS 


•pBocesses 


8t«»  Proc«i«««. 
P««rd  tran.f»r,(duct.) 
cunward  trar.ifer,  (bait} 
upport  I  expo«ur«  of 


The  Energy  for  Photosynthesis.  The  chemical  energy  of  the 
sun's  light,  which  causes  these  two  substances  to  unite,  is  some- 
thing that  we  know  very  little  about,  but  is,  nevertheless,  a  very 
real  and  a  very  great  force.  We  realize  that  the  sun  gives  us  light 
to  see  by,  and  heat  is  evident  enough,  but  when  we  think  of  how 
it  tans  our  skin,  bleaches  our  clothes,  and  makes  our  photographs, 

we  have  some  evidences 
of  the  chemical  action 
of  light,  though  none  of 
these  can  compare  with 
the  work  done  by  these 
same  rays  in  the  leaf 
laboratory,  during  the 
making  of  starch  in  the 
plant. 

This  word  photo- 
synthesis can  now  be 
better  understood,  mean- 
ing as  it  does  "  union  by 
means  of  light,"  since  it 
is  by  the  chemical  power 
of  the  light  rays  that 
the  water  and  carbon 
dioxide  are  united. 

The  leaf  is  sometimes 
compared  to  a  mill  in 
which  the  power  is  the 
sunlight;  the  machinery 
is  the  chlorophyll;  the 

raw  materials  are  the  carbon  dioxide  and  water;   the  product  is 
starch;  and  the  waste  material  is  oxygen. 

The  Waste  Product.  A  benefit  arising  from  photosynthesis 
almost  as  important  as  the  production  of  starch  itself,  is  the  libera- 
tion of  oxygen  as  a  by-product.  We  have  learned  that  every  living 
tissue  breathes  in  oxygen.  The  resulting  oxidation  produces  the 
energy  without  which  we  could  not  live. 


Absorbed  by  root 


lotlc*  th«  connsctlon 
b«tw«tn  root  hair*  and  duett 
thence  to  I.«T»(. 


FIG.  26.     Diagram  of  Plant  Processes. 


LEAF  FUNCTIONS  99 

We  have  also  learned  that  this  oxidation  produces  carbon  di- 
oxide which  we  throw  off  in  respiration.  Now  we  can  see  that  the 
plants  use  this  discarded  carbon  dioxide  for  making  their  food, 
and  return  to  us  the  oxygen  which  is  necessary  for  our  life. 

This  is  a  glimpse  of  one  of  the  great  "  circles  of  nature." 

Other  Leaf  Functions.  Starch  making,  while  the  most  im- 
portant, is  not  the  only  function  of  leaves.  In  their  marvelous 
chemical  laboratory  go  on  the  processes  of  digestion,  proteid  manu- 
facture, assimilation,  respiration,  and  excretion  of  water  (trans- 
piration) .  Digestion  is  necessary  to  put  the  food  stuff  into  soluble 
form  so  that  it  may  act  in  osmosis  and  flow  through  the  ducts. 
As  to  proteid  manufacture,  little  is  known,  except  that  the  carbon, 
hydrogen,  and  oxygen  of  the  starch  are  combined  with  nitrogen, 
sulphur,  and  phosphorus  from  the  soil  water  in  a  way  that  we 
cannot  understand,  much  less  imitate,  and  that  proteids  are  the 
result  of  the  process.  Assimilation  is  active  in  leaves  and  all  other 
living  parts  of  the  plant,  since  this  is  the  process  by  which  the 
nutrients  actually  become  part  of  the  living  protoplasm  and  tissue 
of  the  organism.  Respiration  (oxidation)  goes  on  wherever  liv- 
ing plant  tissue  is  directly  exposed  to  air;  while  less  active  than 
in  animals  the  process  is  just  as  essential,  since  it  supplies  the 
energy  which  keeps  the  plant  alive.  Much  extra  water  is  absorbed 
at  times  by  the  roots,  in  their  transfer  of  nitrogen  compounds  and 
mineral  salts  from  the  soil.  The  useful  elements  are  used  in  food 
making  and  the  surplus  water  is  passed  off  by  way  of  the  spongy 
layer,  air  spaces,  and  stomata.  This  process  is  called  transpiration 
and  differs  from  mere  evaporation,  in  that  the  loss  of  water  is 
regulated  by  the  stomata  and  so  corresponds  to  the  needs  of  the 
plant.  It  does  not  depend  upon  the  temperature  alone,  as  does 
evaporation. 

We  find  in  the  leaf  the  processes  of  food  manufacture,  diges- 
tion, and  assimilation;  these  are  building  up,  or  constructive, 
processes  and  require  a  supply  of  energy  from  the  sun  or  the  living 
protoplasm  to  bring  them  about.  This  food  is  then  united  with 
oxygen,  thereby  releasing  this  sun-given  energy.  It  is  this  energy 
which  keeps  the  plant  alive  and  permits  it  to  grow.  This  last 


100 


BIOLOGY  FOR  BEGINNERS 


process  is,  however,  a  destructive  one  as  far  as  food  and  tissue  are 
concerned  and  necessitates  excretion  in  order*  to  remove  the  waste. 


/too  t  r/ CAT  i  ON  of  FUNCTION 


FIG.  27.     Modification  of  Function  in  Plant  Parts. 

The  circles  at  the  left  represent  the  usual  parts  of  the  plant,  those  at  the 
right,  the  forms  into  which  they  may  be  modified,  to  perform  the  functions 
named. 

The  usual  function  is  connected  with  its  plant  part  by  a  heavy  line; —  those 
less  frequent  by  lighter  lines.  Thus  the  roots'  normal  function  is  absorption, 
but  it  may  be  modified  to  form  tendrils,  spines,  leaf  supports,  or  for  storage,  as 
the  lines  show. 

This  diagram  is  intended  to  show  the  wide  range  of  adaptation  of  struc- 
ture to  function. 

SUMMARY 

1.  Photosynthesis. 

The  manufacture  of  starch  from  carbon  dioxide  and  water. 

2.  Digestion. 

Making  the  food  soluble  by  means  of  plant  enzymes,  such  as, 
Diastase  j  acting  on  sugars  an(j  starches. 

Lipase,  acting  on  fats. 
Pepto-trypsin  acting  on  proteids. 


LEAF   FUNCTIONS 

3.  Assimilation. 

C,  H,  O,  combined  with  N,  S,  P,  etc.,  form  proteids,  etc. 

4.  Respiration. 

Tissue  and  food  plus  oxygen  =  energy  plus  CO2. 

5.  Transpiration. 

Giving  off  large  excess  of  water. 


The  Leaf  as  a  Factory 

The  factory  Green  leaves  (or  other  green  tissue). 

The  work  rooms  The  cells  of  palisade  and  spongy  layers. 

The  machines  Chlorophyll  grains  and  protoplasm. 

The  power  Sunlight. 

Materials  Carbon  dioxide  and  soil  water. 

Supply  department  Root  hairs,  ducts,  air  spaces,  stomates. 

Transportation  dept.  Ducts,  bast  tubes,  pith  rays. 

Finished  products  Starch,  sugar,  proteids,  tissues. 

Waste  product  Oxygen. 

.  I  Manufacturing  dept.  daylight  only. 

Hours  of  work 

{ Transport  and  supply  depts.  day  and  night. 

Comparison  of  Photosynthesis  and  Respiration 

Photosynthesis  Respiration 

Constructive  process  Destructive  process 

Food  and  tissue  accumulated  Food  frnd  tissue  used  up 

Energy  taken  in  from  sun  Energy  released 

Carbon  dioxide  taken  in  Carbon  dioxide  given  off 

Oxygen  given  off  Oxygen  taken  in 

Complex  compounds  formed  Simple  compounds  formed 

Produces  starch,  etc.  Produces  CO2  and  H2O 

Goes  on  only  by  day  Goes  on  day  or  night 

Only  in  presence  of  chlorophyll  In  all  parts  exposed  to  air 

EXPERIMENTS  WITH  LEAVES 

To  show  that  Leaves  (and  Stems)  turn  toward  Light.     Two 
thrifty  plants  are  provided,  one  is  placed  in  a  light-tight  box, 


-102 


"-BIOLOGY  FOR  BEGINNERS 


with  an  opening  at  one  side  for  light  to  enter.  The  other  is  placed 
under  the  same  conditions  of  heat  and  moisture,  but  is  given  light 
from  all  sides. 

The  plant  in  the  box  will  be  found  to  turn  toward  the  light  and 
to  grow  rapidly  in  that  direction.    However,  its  stem  will  be  weaker 


FIG.  28. 

Coleus    leaf    showing    green    and  Similar  leaf  treated  with  iodine,  the 

white  areas,  before  treatment  with       starch   reaction  only  showing  where 
iodine.  the  leaf  was  green.     From  Atkinson. 

and  slenderer,  its  leaves  smaller  and  paler  than  the  one  with 
uniform  lighting. 

This  experiment  shows  the  response  that  plants  make  to  light, 
and  also  the  effect  of  a  limited  supply  of  light  on  their  growth. 
Every  time  we  see  the  leaves  of  house  plants  turning  toward  the 
window,  we  have  a  similar  experiment  in  heliotropism.  The 
plant  kept  outside  the  dark  box  was  used  as  a  check  for  this  ex- 
periment. 


LEAF  FUNCTIONS  103 

Photosynthesis.  To  show  that  Green  Plants  produce  Starch. 
Leaves  can  be  taken  from  active  green  plants,  scalded  to  kill  the 
protoplasm  and  release  the  chlorophyll,  and  soaked  in  alcohol 
to  remove  the  green  color.  Then,  if  tested  with  iodine,  a  dark  blue 
color  is  produced,  showing  that  starch  was  present.  The  chlo- 
rophyll had  to  be  removed  so  that  this  blue  could  be  seen.  This 
proves  that  starch  was  in  the  leaf.  To  prove  that  it  is  made  there,  by 
the  action  of  light  on  the  chlorophyll,  requires  further  experiment. 

To  show  that  chlorophyll  is  necessary,  a  leaf  from  a  green  and 
white-leaved  geranium  may  be  used,  as  above,  when  it  will  be  found 
that  little  starch  is  revealed  in  the  white  portions. 

To  show  that  light  is  necessary,  parts  of  an  active  leaf  are  cov- 
ered with  corks,  pinned  through,  on  both  sides.  After  a  few  days 
the  covered  portions  will  not  yield,  the  starch  test,  while  the  ex- 
posed parts  will  still  do  so.  Another  proof  of  the  same  thing  is 
to  keep  a  plant  entirely  in  the  dark,  as  a  check  experiment,  and 
when  it  has  become  pale,  test  for  starch,  which  will  be  found 
lacking.  Of  course  the  same  kind  of  plant,  under  the  same  con- 
ditions, except  the  light,  should  be  used  in  this  and  in  the  experi- 
ment to  be  compared  with  it. 

To  show  that  Green  Plants  produce  Oxygen.  Oxygen  is  the 
waste  product  of  photosynthesis;  it  is  thrown  off  when  starch  is 
made.  It  is  easier  to  collect  a  gas  over  water,  hence  a  water  plant 
is  used  for  this  experiment,  but  all  green  plants  carry  on  the  same 
process. 

The  water  plant  is  submerged  in  a  glass  jar  under  a  glass  funnel, 
whose  stem  is  covered  by  a  small  test  tube,  filled  with  water  and 
inverted.  The  apparatus  is  set  in  the  sun  and  soon  bubbles  of  gas 
will  rise  in  the  funnel  and  be  collected  in  the  tube.  These,  when 
tested,  prove  to  be  oxygen.  If  carbon  dioxide  be  dissolved  in  the 
water,  the  process  will  go  on  faster,  as  carbon  dioxide  is  one  of 
the  materials  used  in  photosynthesis,  and  that  in  the  jar  of  water 
is  soon  exhausted. 

Another  similar  experiment  ought  to  be  set  up  in  the  dark,  so  as 
to  prove,  again,  that  light  is  the  source  of  energy  for  this  very 
important  process. 


104 


BIOLOGY  FOR  BEGINNERS 


To  prove  that  the  oxygen  did  not  come  from  the  water,  another 
check  could  be  used,  in  which  the  apparatus  was  the  same,  but  no 
plant  was  present,  in  which  case  no  oxygen  would  be  produced. 

In  experimental  work  of  this  kind,  the  check  experiments  show 
almost  as  much  as  the  ones  which  actually  "  work."  Merely  stat- 
ing that  the  water  plant  was  put  under  the  funnel,  and  that  oxygen 

was   produced,   would   not 
prove  anything.     It  would 
be    asked    "  How    do  you 
know  that  the  oxygen  came 
from     the     plant? "     and 
"  How  do  you  know  that 
light  had  anything  to  do  with  the 
process?  "  both  of  which  questions 
are  answered  by  the  "  checks." 

Transpiration.  To  show  that 
Plants  pass  off  Water  Vapor.  A 
thrifty  cutting  is  tightly  sealed  into 
a  bottle  of  water  and  placed  under 
a  bell  jar;  another  similar  bell  jar 
is  set  alongside,  containing  no  plant. 

Water  drops  will  soon  be  seen  on 
FIG.  29.     Bubbles  of  gas  will  rise    .      ... 

in  the  funnel.     From  Atkinson.     the  mslde  of  the  Jar  Wlth  the  Plant> 

none  on  the  other.    As  the  bottle 

was  sealed,  no  water  could  escape,  except  such  as  passed  through 
the  leaves  of  the  plant.  As  the  empty  jar  showed  no  water,  it  did 
not  merely  condense  from  the  air,  hence  must  have  been  passed 
off  by  the  leaves.  A  potted  plant  could  be  used,  but  the  pot  and 
earth  surface  would  have  to  be  wrapped  in  oiled  paper  or  sheet 
rubber,  to  prevent  evaporation. 

To  show  which  surface  of  a  leaf  gives  off  this  water  vapor,  two 
watch  glasses  can  be  fastened,  one  on  either  side  of  a  leaf.  More 
water  will  be  found  to  condense  on  the  glass  fastened  to  the  lower 
surface,  showing  that  transpiration  is  more  active  here.  This  is 
as  one  would  expect,  since  here  the  stomata  are  more  numerous. 

Cobalt  paper,  which  turns  pink  when  moist,  can  also  be  fastened 


LEAF   FUNCTIONS 


105 


to  the  upper  and  lower  surfaces  of  a  leaf,  and  will  show  the  same 
result. 

Thus  the  end  products  of  all  these  processes  are  the  carbon 
dioxide  and  water,  with  which  the  photosynthesis  started.  The 
oxygen  involved  in  the  destructive  processes  is  the  by-product 
of  photosynthesis,  so  that  all  three  elements,  carbon,  hydrogen, 
and  oxygen  pursue  a  circular  course. 


FIG.  30. 


FIG.  31. 


Figure  30  shows  plant  with  pot  sealed,  but  giving  off  water  vapor  which 
has  condensed  on  bell  jar. 

Figure  31.  Left-hand  figure,  shows  plant  with  sealed  pot,  giving  off  water 
vapor  enough  to  turn  the  cobalt  paper  pink  within  fifteen  minutes.  The  right- 
hand  figure  is  a  check  experiment,  to  show  that  the  moisture  in  the  air  would 
not  cause  the  change  in  the  same  time.  From  Atkinson. 


COLLATERAL   READING 

Plant  Relations,  Coulter,  pp.  148-161;  Botany  for  Schools,  Atkinson, 
pp.  90-116;  Elementary  Botany,  Atkinson,  pp.  53-70;  First  Studies  in 
Plant  Life,  Atkinson,  pp.  121-125;  Lessons  in  Botany,  Atkinson,  pp. 
70-72;  Experiments  in  Plants,  Osterhout,  pp.  191-202;  Biology  Text, 
Hunter,  pp.  132-134;  Essentials  of  Biology,  Hunter,  pp.  115-132;  Intro- 
duction to  Biology,  Bigelow,  pp.  55-75;  Plant  Life  and  its  Uses,  Coulter, 
pp.  218-234;  The  Great  World's  Farm,  Gaye,  pp.  157-176;  The  Story  of 
the  Plants,  Allen,  pp.  33-53;  Textbook  of  Botany,  Gray,  pp.  85-110. 


106 


BIOLOGY  FOR  BEGINNERS 


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CHAPTER  XIV 

FLOWERS:      POLLENATION   AND   FERTILIZATION 

Vocabulary 

Pollenation,  transference  of  pollen  from  anther  to  stigma. 
Fertilization,  union  of  sperm  nucleus  and  ovule  nucleus  to  form 

the  embryo. 

Conspicuous,  noticeable. 

Glands,  organs  for  secretion  of  any  liquid,  as  nectar  glands. 
Nectar,  a  sweet  liquid  secreted  by  plants  to  attract  insects.     Bees 

make  it  into  honey;  plants  do  not  secrete  honey. 
Learn  names  of  flower  parts  from  the  text. 

If  we  refer  to  the  list  of  life  functions  it  will  be  seen  that  we 
have  dealt  with  all  of  them  except  reproduction.  All  the  others 
have  had  to  do  with  the  life  of  one  individual  plant,  its  food  getting, 
energy  production,  or  waste  removal.  Now  we  have  to  do  with  a 
function  as  important  as  all  the  rest,  the  propagation  of  new 
individuals. 

The  Function  of  the  Flower.  In  most  of  the  common  plants 
the  flower  is  the  organ  whose  function  is  reproduction,  and,  while 
there  are  other  methods,  we  shall  deal  with  the  commonest  one 
first,  since  it  is  found  in  at  least  130,000  different  kinds  of  plants. 

The  final  product  of  the  flower  is  the  seed.  To  produce  the 
seed,  fertilization  must  take  place  and  to  cause  fertilization,  pol- 
lenation  must  precede  it.  While  these  terms  will  be  made  plain 
later,  we  can  remember  that  the  flower  is  provided  with  means 
for  securing  pollenation,  fertilization,  and  seed  production. 

Structure  of  the  Flower.  We  will  take  for  an  example  the  ge- 
ranium, either  a  "  single  "  flowered  house  species  or  the  common 
wild  geranium,  which  though  different  as  to  genus,  is  still  suffi- 
ciently similar  for  our  purpose.  As  we  look  at  the  flower  from 
the  rear,  or  stem  side,  we  will  see  a  row  of  small  green,  leaf-like 

108 


FLOWERS:  POLLEN ATION   AND   FERTILIZATION     109 


organs  called  the  sepals.  This  is  the  calyx.  Its  function  is  to  pro- 
tect the  flower  in  the  bud  condition  and  to  help  support  the  other 
parts  when  it  opens. 

Inside  the  calyx  comes  the  corolla  consisting  of  a  row  of  colored 
parts  called  petals.     These  are  often  for  the  attraction  of  insects 
as  we  shall  see  when  studying 
pollenation,    and    may    also 
help  to  protect  the  inner  and 
more  essential  parts. 

Next  inside  the  corolla 
we  will  come  to  several 
knobbed,  hair-like  organs. 
These  are  the  stamens.  The 
knobs  at  their  tops  (anthers) 
are  very  important,  as  they 
produce  and  scatter  a  yellow, 
dust-like  substance  known  as 
pollen.  They  are  placed  on 
these  thread-like  supports 
(filaments)  so  that  the  pollen 
will  have  a  better  chance  to 
be  distributed. 

In  the  very  center  of  the 
flower  is  the  pistil  consisting 
of  a  sticky  knob  at  the  top 
(stigma)  to  catch  pollen,  a 

slender  stalk  (style)  to  support  the  stigma,  and  an  enlarged  portion 
at  .the  base  (ovary)  which  contains  the  undeveloped  seeds  (ovules) 
and  later  develops  into  the  fruit. 

Pollenation.  In  order  that  a  flower  may  produce  seed,  the  pollen 
must  be  transferred  from  the  anther  to  the  stigma,  and  usually  it 
must  be  from  the  anther  of  one  flower  to  the  stigma  of  another  of 
the  same  kind.  This  transfer  of  pollen  from  anther  to  stigma  is 
called  pollenation.  If,  as  in  most  cases,  it  is  between  different 
flowers,  it  is  called  cross  pollenation  and  is  the  process  for  which  the 
flower  parts  are  adapted.  Insects  and  wind  are  the  two  chief 


S.     $,**!..  (CM 

P.    ftTAi.,   ft 


STYLt 

OvAftr 

OVULES 


FIG.  32.    The  flower  is  provided  with 
means  for  seed  production. 


110  BIOLOGY  FOR  BEGINNERS 

agents  in  pollenation  and  there  is  no  process  for  which  more  curi- 
ous adaptations  have  been  developed.  We  shall  deal  first  with 
those  that  fit  the  flower  for  pollenation  by  insects. 

Adaptations  for  Insect  Pollenation.  The  bee  and  the  flower  are 
associated  in  our  minds,  of  course,  but  it  is  not  so  commonly  realized 
that  one  could  not  exist  without  the  other,  and  that  many  other 
insects,  besides  bees,  are  just  as  closely  concerned. 

The  insect  comes  to  get  its  food  from  the  sugary  nectar  which 
is  secreted  at  the  base  of  the  petals ;  in  getting  this,  its  body  catches 
some  of  the  pollen  from  the  stamens  which  are  shaped  for  this 
purpose.  When  the  insect  visits  the  next  flower  some  pollen  is  sure 
to  be  rubbed  off  on  the  pistil  of  that  flower,  and  a  new  supply 


FIG.  33.    Hawk-moth  posed  before  a  jimson-weed,  Datura  stramonium  (after 
Stevens;  one-half  natural  size). 

brushed  from  the  stamens  as  it  crawls  out.  In  this  way  pollena- 
tion is  accomplished. 

In  order  that  the  insects  may  surely  see  each  flower,  they  have 
developed  conspicuously  colored  corolla  and  attractive  odors. 
They  often  grow  in  clusters  so  as  to  be  easily  noticed  and  visited. 
After  the  insect  arrives,  not  only  does  it  find  a  reward  of  nectar, 
but  often  the  flower  is  shaped  to  provide  a  convenient  landing 
place.  Colored  lines  lead  to  the  nectar  glands.  Stamens  and 
pistils  hold  their  anthers  and  stigmas  in  just  the  proper  position  so 
that  pollen  shall  be  transferred  while  the  insect  is  obtaining  its 
sweet  reward  for  unintended  labors. 

Nearly  every  flower  has  a  slightly  different  scheme  for  cross 
pollenation.  When  we  find  one  with  irregular-shaped  corolla,  we 


FLOWERS:  POLLENATION  AND   FERTILIZATION     111 

may  be  almost  sure  that  some  special  adaptation  for  insect  visitors 
stands  behind  the  curious  shape. 

Adaptations  for  Wind  Pollenation.  Flowers  which  depend  on 
wind  for  their  pollenation  are  very  differently  adapted.  They 
produce  enormous  quantities  of  pollen,  but  they  have  no  nectar 
or  odor.  Their  pistil  is  usually  large  to  catch  the  flying  pollen, 
and  they  secure  access  to  the  wind  by  having  very  small  corollas 
and  by  producing  their  flowers  above  the  leaves  of  the  plant. 


FIG.  34.     Salvia-flower. 

A,  showing  position  of  pistil  and  stamens; 

B,  anthers  of  stamens  in  normal  position; 

C,  anthers  of  stamens  tipped  down; 

D,  bee  entering  flower; 

E,  flower,  natural  condition. 

(After  Lubbock,  natural  size.) 

Many  grasses  and  sedges  and  all  the  evergreen  trees  have  their 
pollen  distributed  by  the  wind.  In  fact,  near  large  pine  forests 
the  yellow  pollen  fills  the  air  and  covers  the  ground  at  certain 
seasons,  forming  what  people  call  "  sulphur  showers." 

Protection  of  Pollen.  Since  pollen  is  absolutely  necessary  to  the 
plant,  it  has  to  be  protected  from  rain  and  from  insects  which 
would  eat  it  and  from  those  which  are  too  small  or  too  smooth- 
bodied  to  carry  it.  Protection  against  rain  and  dew  is  secured  by 
the  drooping  or  closing  of  the  corolla,  while  unwelcome  insect 


112  BIOLOGY  FOR  BEGINNERS 

visitors  are  kept  out  by  hairy  or  sticky  coatings  on  stem  and 
calyx  or  on  the  inside  of  the  corolla. 
Essential  Organs.    Notice  that  the  only  organs  absolutely  needed 


FIG.  35.    Spartium,  showing  the  dusting  of  the  pollen  through  the  opening 
keels  on  the  under  side  of  an  insect.    (From  Kerner  and  Oliver,  see  Kellogg.) 

to  produce  seeds  are  the  stamens  and  pistil.  Hence  they  are  called 
the  "  essential  organs."  The  corolla  and  calyx  have,  as  their 
function,  the  protection  of  these  essential  organs  and  the  securing 
of  pollenation. 


FLOWERS:  POLLENATION   AND    FERTILIZATION     113 

The  pollen  grain  from  the  anther  and  the  ovule  in  the  ovary 
are  actually  the  most  necessary  factors  in  the  process  of  reproduc- 
tion and  must  now  be  dealt  with  more  completely. 


FIG.  36.     Seed  Development. 

Part  I.     Pollenation 

Fig.  1.  The  stamen  is  shown  with  part  of  the  filament,  and  the  anther  open- 
ing to  set  free  the  pollen.  This  may  be  transported  either-by  wind  or  insects, 
to  the  stigma  of  the  pistil  of  a  similar  kind  of  flower,  shown  in  Fig.  2. 

After  arriving  there,  the  pollen  develops  a  long  tubular  cell  which  reaches 
clear  to  the  ovary,  down  the  whole  length  of  the  style,  even  though  it  be  as 
long  as  a  "silk"  of  corn. 

The  development  of  this  tube,  and  the  passage  of  the  sperm  nucleus  from 
the  pollen,  down  it,  are  shown  here,  though  they  are  really  steps  in  fertilization. 
Pollenation  is  really  the  mere  transfer  of  the  pollen. 

Part  II.     Fertilization. 

Fig.  1.  The  pollen  tube  is  entering  the  micropyle  and  the  sperm  nucleus  is 
at  its  lower  end.  Note  the  ovule  nucleus,  with  which  it  is  to  unite.  Both  one- 
celled  stages. 

Fig.  2.  The  sperm  nucleus  has  passed  out  of  the  pollen  tube  and  is  approach- 
ing the  ovule  nucleus. 

Fig.  3.  The  sperm  and  ovule  nuclei  have  united; —  this  is  the  actual  fer- 
tilization, from  which  the  development  of  the  embryo  begins. 

Fig.  4,  5  and  6  show  stages  in  the  early  cell  divisions  as  the  embryo  develops. 

Fig.  7  shows  the  matured  seed.  The  parts  of  the  embryo  have  gone  as  far 
as  they  will  till  germination  commences.  Extra  stored  food  remains  unused 
outside,  as  endosperm. 


114  BIOLOGY  FOR  BEGINNERS 

Pollen  Structure.  The  pollen  grain  is  at  first  a  single  cell  but 
if  transferred  to  the  stigma  of  a  flower  of  its  own  kind,  it  begins  to 
grow,  forming  three  cells,  one  of  which  develops  into  a  very  long 
tube  which  reaches  from  stigma  to  ovary,  no  matter  how  long 
that  may  be.  The  other  two  cells,  containing  the  most  active 
kind  of  protoplasm,  are  called  the  sperm  or  male  cells,  and  their 
union  with  the  ovule  is  called  fertilization  and  produces  the 
embryo  in  the  seed. 

Ovule  Structure.  The  ovules  (undeveloped  seeds)  are  protected 
inside  the  ovary  and  can  be  reached  only  by  way  of  the  pollen  tube 
from  pollen  grains  on  the  stigma.  They  are  much  larger  and  more 
complicated  than  the  pollen  grains.  Each  ovule  in  the  ovary  has 
a  protective  covering  which  later  becomes  the  testa  of  the  seed. 
Within  this  is  the  nucleus  of  the  ovule  cell  which  divides  into  eight 
cells,  two  of  which  form  the  endosperm  and  one,  the  most  im- 
portant, becomes  the  egg  or  female  cell.  As  has  been  said,  the 
pollen  tube  grows  downward  through  the  style  till  it  reaches  the 
place  where  an  ovule  is  attached  to  the  ovary  wall ;  near  this  point 
of  attachment  is  an  opening  through  the  ovule  coats,  called  the 
micropyle,  and  through  this  the  pollen  tube  makes  its  way  till  it 
reaches  the  egg  cell  within. 

Fertilization.  The  sperm  cell  then  passes  down  the  pollen  tube 
and  unites  with  the  protoplasm  of  the  egg  nucleus.  This  union  of 
the  sperm  nucleus  of  the  pollen  with  the  egg  nucleus  of  the  ovule 
is  called  fertilization.  The  fertilized  egg  now  has  the  very  re- 
markable power  to  grow,  and  from  its  one  cell,  to  develop  the 
countless  numbers  which  go  to  make  up  the  embryo  within  the 
seed  and  finally  the  whole  new  plant.  Notice  that  in  this  wonder- 
ful process  each  plant  is  reduced  to  a  single  cell,  the  sperm  or 
the  egg,  —  that  they  unite  and  again  form  a  single  cell,  and  that 
from  this  develop  the  embryo  and  the  whole  organism. 

Fertilization  is  essentially  the  same  in  both  plant  and  animal  so 
you  must  try  to  think  of  all  living  things  as  having  developed  from 
a  single  fertilized  egg  cell. 

Origin  of  Seed  Parts.  Look  back  at  Chapter  VI  and  notice 
that  we  have  just  been  studying  the  origin  of  all  parts  mentioned 


FLOWERS:  POLLENATION  AND   FERTILIZATION     115 

in  the  structure  of  the  seed:  the  ovule  walls  become  the  testa  and 
tegumen;  the  opening  for  the  pollen  tube  is  the  micropyle;  the 
fertilized  egg  develops  into  the  embryo,  and  the  endosperm  nuclei 
produce  the  endosperm. 

The  embryo  may  develop,  to  a  great  extent  within  the  seed  and 
use  all  the  endosperm,  or  it  may  develop  but  little  and  leave  un- 
used endosperm  for  the  germination  process.  In  either  case  it  was 
present  at  one  time. 

Notice  that  the  seed  stage  is  only  a  pause  in  the  continuous 
circle  of  growth.  The  parent  plants  produce  the  pollen  and  ovules; 
these  produce  sperm  and  egg;  both  grow  and  finally  unite.  The 
embryo  is  formed  and  grows  more  or  less  within  the  seed,  then 
merely  waits  and  rests  till  it  shall  have  conditions  favorable  for 
continuing  its  growth  to  an  adult  plant,  again.  In  this  way  the 
life  cycle  is  completed.  The  parents  die  but  parts  of  their  actual 
protoplasm  live  on,  forever,  in  the  new  generation. 

COLLATERAL   READING 

POLLENATION 

Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom,  Darwin;  The 
Great  World's  Farm,  Gaye,  pp.  208-214;  With  the  Wild  Flowers,  Hardinge, 
pp.  47-55;  Ten  New  England  Blossoms,  Weed,  pp.  1-17,  90-98;  Beauties 
of  Nature,  Lubbock,  pp.  117-138;  The  Fairy  Land  of  Science,  Buckley, 
p.  212-237;  Elementary  Studies  in  Botany,  Coulter,  pp.  151-166;  Plant 
Life  and  Uses,  Coulter,  pp.  301-322;  Natural  History  of  Plants,  Kerner 
and  Oliver,  Vol.  II,  Part  1,  pp.  129-283,  426-436,  Part  2,  833-840,  862-866; 
Experiments  in  Plants,  Osterhout,  pp.  286-311;  Plants  and  their  Children, 
Dana,  pp.  187-255;  The  Living  Plant,  Ganong,  pp.  303-326;  Practical 
Biology,  Smallwood,  pp.  296-308;  The  Story  of  Plants,  Allen,  pp.  73-135; 
Outline  of  Botany,  Leavitt,  pp.  120-127;  Textbook  of  Botany,  Bessey, 
p.  421;  Textbook  of  Botany,  Strasburger,  pp.  281-283;  Plant  Rela- 
tions, Coulter,  pp.  123-137;  .  Introduction  to  Botany,  Stevens,  pp. 
166-201;  Plant  Structures,  Coulter,  p.  181;  Nature  and  Work  of 
Plants,  McDougal,  pp.  149-153;  Lessons  in  Botany,  Atkinson,  pp.  192- 
193;  Elementary  Botany,  Atkinson,  pp.  351-367;  Botany  for  Schools, 
Atkinson,  pp.  167-181;  Elementary  Biology,  Peabody  and  Hunt,  pp. 
74-88;  Flowers,  Fruits  and  Leaves,  Lubbock,  pp.  1-44;  Plant  Life,  Step, 
pp.  35-58;  Wonders  of  Plant  Life,  Herrick,  pp.  149-173;  Blossom  Hosts 
and  Insect  Guests,  Gibson,  entire;  Flowers  and  their  Friends,  pp.  121-133; 
231-239;  Fertilization  in  the  Vegetable  Kingdom,  Darwin,  pp.  356-414, 


116  BIOLOGY  FOR  BEGINNERS 

FERTILIZATION 

Botany  for  Schools,  Atkinson,  pp.  182-186;  Elementary  Biology,  Peabody 
and  Hunt,  pp.  74-88. 

FLOWER  STRUCTURE 

Plant  Structures,  Coulter,  pp.  218-231;  Lessons  with  Plants,  Bailey,  pp. 
131-150;  Botany  for  Schools,  Atkinson,  pp.  140-166;  Elementary  Biology, 
Peabody  and  Hunt,  pp.  70-74;  Plant  Life  and  Uses,  Coulter,  pp.  258-300; 
Applied  Biology,  Bigelow,  pp.  196-213. 

SUMMARY 

Function  of  flower,  reproduction  by  means  of  seeds. 
Steps  in  seed  production. 

1.  Pollenation. 

2.  Fertilization. 

3.  Growth  of  embryo  in  seed. 

Flower  parts.  Function. 

Calyx  (sepals)  Protection  and  support. 

Corolla  (petals)  Insect  attraction  for  pollenation. 

Protection  of  essential  organs. 
Stamens, 

Anther  Production  of  pollen. 

Filament  Support  of  anther  for  pollenation. 

Pistil, 

Stigma  To  catch  pollen:  sticky,  sometimes 

large. 
Style  To  support  stigma  so  as  to  catch 

pollen. 
Ovary  Contains  ovules,  forms  fruit. 

Pollenation. 

Definition.     Meaning  of  "cross-pollenation." 
Means  for  pollenation: 
Insects  (clover,  etc.) 

Adaptations  for  insect  pollenation. 
.     Nectar,  Odor, 

Bright  color,  Growth  in  clusters, 

Landing  places,  Special  shapes. 

Wind  (pine,  corn,  grasses,  etc.) 
Adaptations  for  wind  pollenation. 

Flowers  high  above  leaves,  not  conspicuous. 
Petals  and  sepals  small  or  lacking. 
Pistils  large  and  sticky. 
Abundant  pollen  (why?) 
No  nectar  nor  odor. 


FLOWERS:  POLLENATION   AND    FERTILIZATION      117 

Pollen  protection. 

From  rain  by  closing  or  drooping  of  flower. 

From  unwelcome  insects  by  sticky  stems  or  hairy  flowers. 

Essential  organs. 
What  are  they? 
Why  so  called? 

Fertilization. 

Definition:   union  of  sperm  nucleus  of  pollen  with  egg  nucleus  of  the  ovule. 

Pollen. 

1.  Produced  by  stamen  (anther). 

2.  Structure:   one-cell  stage. 
Three  cell  stage. 

Pollen  tube  (use  ?). 
Sperm  cells  (use  ?). 
Ovule. 

1.  Produced  in  the  ovary:  undeveloped  seed. 

2.  Structure:  coverings  (seed  coats  later). 

One-cell  stage. 
Eight-cell  stage. 

Two  cells  from  endosperm.      * 

One  forms  egg  cell,  proper. 

Fertilization. 

1.  Pollen  tube  penetrates  micropyle. 

2.  Sperm  cell  passes  down  pollen  tube. 

3.  Nuclei  of  sperm  and  egg  unite  (fertilization  proper). 

4.  Embryo  begins  to  develop. 

Origin  of  seed  parts. 

1.  Ovule  walls  become  seed  coats. 

2.  Opening  for  pollen  tube  is  the  micropyle.' 

3.  Fertilized  egg  becomes  the  embryo. 

4.  Endosperm  nuclei  become  the  endosperm. 

Endosperm  may  be  used  by  developing  embryo. 
Endosperm  may  remain  to  be  used  in  germination. 


CHAPTER  XV 
FRUITS  AND  THEIR  USES 

Vocabulary 

Matured,  fully  developed. 
Infinite,  endless. 
Superficial,  careless. 
Relatively,  comparatively. 

While  the  seeds  are  developing,  the  ovary  grows  also,  and  the 
final  result  is  what  we  call  a  fruit.  This  does  not  necessarily  mean 
"  fruit "  in  the  sense  of  a  fleshy  edible  product,  but  applies  to 
the  seed-holding  organ  of  any  plant.  A  fruit  may  be  denned  as 
the  matured  ovary,  its  contents,  and  all  intimately  connected 
parts.  Thus  a  fruit  may  consist  of  a  single  ovary  with  only  one 
seed,  as  in  grains,  nuts,  cherries,  or  plums,  or  it  may  develop  from 
a  single  ovary  which  has  several  seeds,  as  in  pansy,  pea,  poppy, 
or  apple.  On  the  other  hand  there  are  many  flowers  which  have 
several  ovaries.  These  combine  to  form  compound  fruits  like  the 
strawberry  or  raspberry.  Fruits  may  therefore  be  either  dry  or 
fleshy,  simple  or  compound,  depending  on  the  character  and  de- 
velopment of  the  ovary  which  formed  them. 

Types  of  Fruits.  The  peach  is  a  good  example  of  a  one-celled, 
simple,  fleshy  fruit.  In  it  the  ovary  wall  develops  two  parts,  an 
outer  fleshy  layer  and  the  hard  inner  "  stone  "  which  encloses  the 
seed.  Such  a  fruit  is  called  a  stone  fruit. 

The  apple  develops  from  a  five-celled  ovary  which  forms  the 
core.  Outside  of  this  is  a  fleshy  region,  usually  bounded  by  a  faint 
line  which  is  probably  the  fleshy  ovary  wall,  or  may  be  an  enlarged 
receptacle.  Outside  of  this  is  the  bulk  of  the  apple,  which  is  a 
greatly  thickened  calyx,  as  is  indicated  by  the  five  tiny  sepal  tips 
which  persist  at  the  blossom  end.  Inside  these  tips  the  dried  sta- 

118 


FRUITS  AND  THEIR  USES  119 

mens  and  pistil  may  sometimes  be  found.  A  section  through  an 
apple  shows  the  outer  skin,  the  calyx  layer,  the  fleshy  ovary  wall, 
the  hard  ovary  wall  and  the  seeds  attached  to  the  central  axis, 
with  their  points  toward  the  stem.  A  fruit  of  this  type  is  called 
a  pome  and  is  represented  by  the  apple,  pear,  quince,  and 
medlar. 

The  bean  pod  is  a  type  of  a  many-seeded  dry  fruit,  called  a 
legume.  At  the  stem  end  may  be  found  the  remains  of  the  calyx 
lobes.  The  bulk  of  the  pod  is  the  ovary;  the  pointed  tip  is  the  style, 
on  which  the  stigma  may  sometimes  be  found  in  young  pods,  as  a 
tiny  knob.  The  "  string  "  is  a  vascular  bundle  bringing  nourish- 
ment to  the  growing  ovules,  which  are  attached  along  one  side  of 
the  pod.  Their  point  of  attachment  is  called  the  placenta,  and  the 
scar  left  on  the  seed,  when  it  is  removed,  is  the  hilum.  The  bean 
fruit  thus  includes  mainly  the  greatly  enlarged  ovary  and  its  con- 
tents, with  the  style  and  possibly  the  stigma  also.. 

Functions  of  Fruits.  The  chief  functions  of  fruits  are  to  protect 
the  ovules  and  seeds  from  attack  by  insects,  or  fungous  spores;  to 
prevent  loss  of  water;  and  to  provide  for  dispersal.  To  provide 
for  these  purposes  the  ovary  develops  in  various  ways.  Tufts  of 
hair,  wings,  or  hooks  may  be  produced  to  aid  in  dispersal.  Tough 
shells  or  rinds  may  form  for  protection  as  in  nuts  or  lemons.  De- 
licious flesh  may  envelop  the  hard  inner  stone,  tempting  animals 
to  eat  the  fruit  and  discard  the  seed  at  a  distance  from  the  parent 
tree.  The  peach  or  cherry  are  examples  of  this.  In  addition  to 
the  developments  of  the  ovary  wall,  the  calyx  may  become 
fleshy  and  envelop  the  ovary  as  in  apples  and  pears.  In  other 
cases  the  end  of  the  stem  (receptacle)  enlarges  and  becomes 
a  part  of  the  fruit,  as  in  the  case  of  the  strawberry  and 
blackberry. 

Seed  Dispersal.  That  the  ovary  wall  protects  the  seeds  from 
insect  attack,  drought,  decay,  and  weather  is  plain  enough,  but 
how  the  other  function,  dispersal,  is  accomplished  may  not  be  so 
evident.  The  most  superficial  observation  of  any  common  plant, 
such  as  the  dandelion,  will  reveal  two  facts:  (1)  an  enormous  num- 
ber of  seeds  are  produced  and  (2)  each  full-grown  plant  requires  a 


120 


BIOLOGY  FOR  BEGINNERS 


FIG.  37.    Fruit  Structure. 

Figs.  1  and  2.  The  Apple.  —  These  drawings  are  diagrammatic,  but  intend 
to  show  the  origin  and  structure  of  the  regions  in  one  of  the  more  complicated 
fleshy  fruits. 

The  outer  region,  (A)  is  probably  the  greatly  thickened  calyx,  as  the  per- 
sistance  of  the  five  calyx  tips  at  the  blossom  end  would  indicate.  However 
some  botanists  consider  it  to  be  an  enlarged  end  of  the  stem  called  the  re- 
ceptacle, which  has  carried  up  the  calyx  lobes  with  its  growth. 

The  region  (B)  shows  in  most  apples  by  being  separated  from  (A)  by  a  faint 
line  or  row  of  dots.  This  is  the  fleshy  outer  wall  of  the  ovary.  Inside  of  this 
region  is  where  "water  cores"  sometimes  develop. 

(C)  is  the  real  "core"  of  the  apple,  tough  and  leathery  enclosing  the  seeds(D). 
This  core  has  five  chambers  or  cells  enclosing  one  or  more  seeds.  Running 
through  the  center  is  a  tough  axis  to  which  the  seeds  are  attached,  with  their 
points  toward  the  stem  end. 

These  same  parts  are  shown  in  the  cross  section,  and  the  seeds  are  cut  in 
two  which  shows  the  two  cotyledons  in  each. 

In  the  cavity  at  the  blossom  end  may  sometimes  be  found  the  dried  up 
remains  of  the  stigma  and  stamens. 

The  parts  included  in  the  apple  are  the  calyx  and  ovary  at  least,  and  pos- 
sibly others. 


FRUITS  AND  THEIR  USES  121 

Figs.  3  and  4.  The  Bean.  —  This  is  a  typical  dry  fruit  with  several  seeds, 
which  opens  to  scatter  them. 

It  consists  of  the  fully  developed  pistil,  the  bulk  being  the  greatly  enlarged 
ovary,  with  the  stigma  reduced  to  the  tapering  tip,  and  the  stigma  usually 
fallen  off  in  a  fully  matured  pod. 

The  "string"  which  we  remove  in  preparing  for  food,  is  a  duct  bundle  that 
brought  nourishment  to  the  ovules  and  reached  each  by  way  of  the  hilum. 

The  point  of  attachment  to  the  pod  is  the  placenta,  (P)  and  shows  in  both 
drawings. 

The  pod  is  the  thickened  ovary  wall  (O),  and  at  its  base  the  shriveled  calyx 
is  sometimes  found. 

The  cross  section  shows  a  seed  cut  across,  displaying  the  seed  coats  (C), 
and  the  two  cotyledons  (Cot.). 

relatively  large  amount  of  room.  Evidently,  then,  the  seeds  must 
be  scattered  if  they  are  to  survive,  and  usually  those  plants  pro- 
ducing most  seeds  or  needing  most  room  best  attend  to  this  matter 
of  seed  dispersal.  There  is  scarcely  a  more  interesting  chapter  in 
biology  than  this  one  which  deals  with  the  wonderful  adaptations 
by  which  seeds,  though  having  no  power  of  locomotion,  still  manage 
to  transport  themselves  long  distances  and  in  great  numbers. 
Plants  use  the  wind,  water,  animals,  and  various  mechanical 
schemes  to  scatter  their  seeds.  Sometimes  it  is  the  seed  by  itself 
which  is  transported,  sometimes  the  whole  fruit,  but  the  end  is  the 
same,  to  get  a  new  place  where  there  shall  be  space,  food,  light, 
and  moisture  for  the  development  of  the  waiting  embryo. 

Adaptation  for  Wind  Dispersal.  Adaptations  for  wind  dispersal 
are  found  in  the  tufts  of  down  on  thistle  and  dandelion  fruits  and 
milkweed  seed,  in  the  wings  on  the  fruits  of  elm,  ash,  or  maple,  or 
on  the  seeds  of  the  catalpa  or  pine. 

Adaptations  for  Dispersal  by  Animals.  Burs  and  hooks,  as  in 
burdock  and  "  pitchforks,"  enable  the  fruits  to  steal  rides  on 
animals  and  man,  and  get  themselves  picked  or  shaken  off  at  great 
distances.  The  delicious  flesh  of  peach  or  apple,  grape  or  berry  is 
merely  a  sort  of  bribe  to  reward  some  animal  for  carrying  off  the 
fruit.  The  seeds  of  all  such  are  indigestible  and  so  are  carried  far 
from  the  parent  plant.  It  is  noteworthy  that  unripe  fruits  are  usu- 
ally poisonous  or  bad  tasting.  Thus  they  are  not  eaten  before 
the  seed  is  ready  for  dispersal. 


122 


BIOLOGY  FOR  BEGINNERS 


Seed  dispersal. 


No.  1.  Maple  "key,"  one  of  a  pair  of  fruits  which  separate  as  they  fall. 
They  whirl  in  a  horizontal  plane,  and  so  fall  slowly  and  are  blown  to  some  dis- 
tance. The  heavy  end  works  down  to  the  ground,  giving  the  enclosed  seed  a 
chance  to  germinate. 

No.  2.  Pine  seed.  Not  a  fruit,  like  the  maple,  though  dispersed  in  the 
same  way.  Shaken  out  of  the  cone  when  ripe. 

No.  3.  The  Bass-wood.  A  group  of  fruits,  with  a  parachute  which  lets 
them  fall  slowly  and  so  reach  some  distance,  also  it  will  drag  them  some  farther 
after  alighting,  especially  on  a  "crust"  in  the  winter. 

No.  4,  Clematis  and  No.  5,  the  Dandelion,  are  both  fruits  with  parachutes 
made  of  downy  hairs.  The  Milkweed  has  a  similar  device  on  its  seed. 

No.  6,  the  Bladder-nut  and  No.  7,  a  Sedge,  are  both  provided  with  water- 
tight life  preservers,  which  float  the  seeds  to  distant  landing  places.  Bladder- 
nut  is  also  light  enough  to  blow. 

No.  8.  The  Poppy  fruit,  has  many  tiny  openings  at  the  top  of  its  "pepper 
box"  capsule.  The  stem  is  stiff  and  springy  and  the  small  heavy  seeds  whip 
out  in  the  wind,  a  few  at  a  time,  assuring  at  least  some  of  them,  favorable 
conditions. 


FRUITS  AND  THEIR  USES  123 

No.  9.  The  Pea,  a  type  of  all  the  family,  which  throws  out  the  seeds  by  the 
twisting  of  the  pod,  as  it  dries. 

No.  10.    The  Wild  Geranium,  slings  its  seeds,  as  the  pod  splits  upward. 

No.  11,  the  Violet  and  No.  14,  the  Witch-hazel,  pinch  their  seeds  out,  as  the 
pod  dries  and  closes  together. 

No.  12,  the  "Pitch-fork"  and  No.  13,  Desmodium,  catch  on  animals,  by 
their  hooks,  and  are  thus  scattered. 

Dispersal  by  Water.  A  considerable  number  of  plants  secure 
dispersal  by  having  fruits  that  float,  without  absorbing  water, 


FIG.  39.     Milkweed  (Asdepias  cornilu)  dissemination  of  seed.     From 

Atkinson. 

and  so  are  carried  by  rivers  or  ocean  currents  to  favorable  places 
along  the  shore.  Sedges  and  coconuts  are  examples  of  this  type. 
Mechanical  Dispersal.  Some  of  the  most  curious  adaptations  for 
seed  dispersal  are  the  mechanical  devices  by  which  seeds  are  thrown 
from  the  pods  for  a  considerable  distance.  The  touch-me-not, 


124 


BIOLOGY  FOR  BEGINNERS 


whose  pod  explodes  when  ripe;  the  witch  hazel,  which  pinches 
the  seed  between  the  open  ovary  walls  till  it  shoots  out;  the  tall 
stalked  mullein  and  poppy,  which  whip  in  the  wind  and  sling  their 
fine  heavy  seeds  far  away  are  examples  of  this  interesting  type. 


FIG.  40.     Seed  distribution  of  Virgin's  Bower  (clematis).     From  Atkinson. 

Economic  Importance  of  Fruits.  So  far  as  the  plant  is  concerned, 
the  object  of  the  fruit  is  to  secure  reproduction  by  providing  the 
enclosed  seeds  with  protection  and  transportation.  However,  man 
has  learned  to  depend  upon  fruits  for  food  and  other  uses,  so 


FRUITS    AND    THEIR    USES  125 

that   they  are   the   most  important  part  of   the  plant  for   his 
purposes. 

To  begin  with,  we  must  remember  that  the  grains,  such  as  wheat, 
rice,  and  corn,  are  fruits  and  not  merely  seeds  as  we  commonly 
think.  These  furnish  more  food  than  all  other  plant  parts,  com- 
bined. Then  there  are  the  fleshy  fruits  —  like  the  apple,  orange, 
grape,  and  peach  —  which  we  use  raw,  cooked,  and  canned,  and 
from  which  many  other  food  products  are  manufactured.  From 
the  downy  contents  of  the  cotton  boll  we  obtain  that  most  essential 
fiber,  which  nature  intended  to  help  in  dispersing  the  seed. 

On  the  other  hand,  the  fruits  of  some  weeds  are  altogether  too 
efficient  in  their  methods  of  dispersal,  and  we  have  to  fight  the 
spread  of  plants  like  the  dandelion,  hawk  weed,  burdock,  and 
thistle.  Some  fruits  are  poisonous,  presumably  better  to  protect 
the  seeds,  and  these  occasionally  do  harm  to  man;  among  them 
may  be  mentioned  the  Jimson  weed,  night-shade,  and  water  hem- 
lock. 

COLLATERAL   READING 

Seed  Dispersal,  Beal,  entire;  Little  Wanderers,  Morley,  entire;  Plant 
Relations,  Coulter,  pp.  112-122;  Introduction  to  Botany,  Stevens,  pp. 
207-217;  Plant  Structures,  Coulter,  pp.  210-215;  The  World's  Great  Farm, 
Gaye,  Chap.  17  and  18;  Textbook  of  Botany,  Strasburger,  pp.  288-291; 
Lessons  in  Botany,  Atkinson,  pp.  292-299;  Elementary  Botany,  Atkinson, 
pp.  368-373;  Lessons  with  Plants,  Bailey,  pp.  336-341;  Plants  and  their 
Children,  Dana,  pp.  50-73;  Botany  for  Schools,  Atkinson,  pp.  198-205; 
Flowers,  Fruits  and  Leaves,  Lubbock,  pp.  45-96;  Natural  History  of  Plants, 
Kerner  and  Oliver,  Vol.  II,  Part  2,  pp.  833-878;  Elementary  Studies  in 
Botany,  Coulter,  pp.  167-186;  Experiments  in  Plants,  Osterhout,  pp.  312- 
325;  With  the  Wild  Flowers,  Hardinge,  pp.  202-216;  The  Story  of  the 
Plants,  Allen,  pp.  149-161;  The  Living  Plant,  Ganong,  pp.  378-402. 

SUMMARY 

1.  Definition  of  Fruit 

2.  Types  of  fruits. 

Stone  fruit,  one-celled,  fleshy  (peach). 
Pome,  many -celled,  fleshy  (apple). 
Grain  or  nut,  one-celled,  dry  (corn,  pecan) 
Legume,  many-celled,  dry  (bean). 

3.  Functions  of  fruits. 

Protection. 
Dispersal. 


126  BIOLOGY  FOR  BEGINNERS 

4.  Dispersal. 

Reason  for  dispersal. 
Means  of  dispersal: 

1.  Wind,  adaptations  for  wind  dispersal. 

Tufts  of  down  (dandelion,  thistle). 
Wings  (maple,  ash,  elm). 

2.  Animals,  adaptations  for  animal  dispersal. 

Burs  (burdock). 

Hooks  ("pitchforks"). 

Edible  flesh  (peach). 

Hard  or  bitter  "pits"  (why?) 

Bad  tasting  when  unripe  (why?) 

3.  Water. 

4.  Mechanical  devices. 

Explosive  fruits  (touch-me-not). 
Pinching  fruits  (witch  hazel). 
Whipping  fruits  (poppy,  mullein). 

5.  Economic  Importance. 

Plant  propagation. 

Food  supply  (cereals  and  fleshy  fruits). 

Cotton  fiber. 

Harmful  weed  seeds. 

Poisonous  fruits. 


CHAPTER  XVI 

SPORE-BEARING  PLANTS 

Vocabulary 

Complicated,  not  simple  in  structure. 

Parasite,  plant  or  animal  which  obtains  nourishment  at  the  ex- 
pense of  another. 
Scavengers,  destroyers  of  waste  matter. 

The  majority  of  plants  with  which  we  are  familiar  obtain  food, 
grow  and  reproduce  by  root,  leaf,  flower,  and  fruit,  just  as  we 
have  been  learning,  but  there  are  a  large  number  of  important, 
but  less  conspicuous,  forms  that  have  no  flowers,  and  so  produce 
no  seeds.  These  flowerless  plants  reproduce  by  single  cells  called 
spores  which,  by  a  more  or  less  complicated  process,  develop  into 
the  plant  again. 

Classification  of  Spore  Plants.  The  simplest  of  these  flower- 
less  plants  are  the  algae,  which  may  consist  of  only  one  cell  as  in 
pleurococcus  which  forms  the  green  coating  often  seen  on  stones, 
bark,  and  old  fences,  or  they  may  grow  to  large,  many  celled  forms, 
such  as  the  sea  weeds,  or  from  the  green  mats  of  pond  scum 
(Spirogyra)  that  cover  our  ponds.  The  fungi  are  another  large 
group  of  spore  plants  which  have  no  chlorophyll  and  hence  have 
to  depend  on  other  plants  or  animals  for  organic  food.  They  are 
parasites,  and  among  them  we  find  mushrooms,  puff  balls,  moulds, 
yeast,  and  bacteria.  The  next  group,  lichens,  are  really  organisms 
consisting  of  algae  and  fungi  living  together  as  one  plant  and  are 
familiar  as  the  variously  colored,  flat,  scaly  forms  that  grow  in 
patches  on  rocks  and  trees.  More  familiar  still  are  the  mosses 
forming  the  green  carpet  of  the  woods,  and  finally  we  come  to  the 
largest  and  most  complicated  of  the  spore  plants,  the  ferns  and 
their  relatives,  the  horse-tails  and  ground-pines. 

127 


128 


BIOLOGY  FOR  BEGINNERS 


While  it  is  not  necessary  to  learn  these  names  or  figures,  the  fol- 
lowing table  will  show  you  how  large  and  varied  the  plant  kingdom 
really  is  and  how  few  we  know  of  its  members. 


FIG.  41.    Rock  lichen  (Parmelia  contigua).    From  Atkinson. 

Flowering  plants,  spermatophytes  (producing  seeds) : 

True  flowering  plants  and \ 

Pines  and  their  relatives /  130'00 

Flowerless  plants  (producing  spores) 96,600  kinds 

Thallophytes  (algae  and  fungi) : 

Algae 16,000  kinds 

Fungi v 55,000  kinds 

Bryophytes  (mosses  and  their  relatives) 16,500  kinds 

Lichens 5,600  kinds 

Ferns 3,500  kinds 


SPORE-BEARING   PLANTS  129 

The  Fungi.  With  the  exception  of  the  fungi,  all  these  plants 
have  chlorophyll  and  so  can  make  their  own  starch  foods;  but 
this  particular  group  has  developed  the  habit  of  taking  its  food 
from  other  plants  or  animals,  either  dead  or  alive,  and  so  are  called 
parasites.  This  parasitic  habit  crops  out  occasionally  in  the 
flowering  plants,  also,  such  as  the  Indian  pipe  and  beech  drops 
but  they,  as  well  as  all  the  fungi,  pay  a  twofold  penalty  for  their 
laziness. 

Results  of  Parasitic  Habit.  When  a  plant  or  animal  ceases  to 
use  an  organ  that  organ  degenerates,  and  the  plant  or  animal 
loses  the  ability  to  use  it.  So  it  is  with  the  fungi;  they  can  no 
longer  make  their  own  organic  food,  and  are  totally  dependent  on 
others  for  their  life.  They  have  to  produce  millions  of  spores, 
since  only  a  few  can  hope  to  survive. 

Many  fungi  perform  a  useful  function  in  nature  by  using  dead 
organic  tissue  for  their  food,  thus  acting  as  scavengers.  They 
also  convert  such  useless  matter  into  food  materials  which  the 
higher  plants  can  use  again.  Fungi  that  feed  on  dead  organic 
tissue  may  be  useful  as  scavengers,  but  unfortunately  this  dead 
tissue  may  also  be  needed  by  man  for  food.  The  fungi  that  at- 
tack our  stored  meats  and  vegetables  cause  a  great  deal  of  loss 
and  expense. 

Because  of  this  habit,  the  fungi  bear  a  peculiar  and  important 
relation  to  other  plants  and  animals,  and  especially  to  man.  There- 
fore we  shall  deal  with  them  as  an  example  of  the  spore-producing 
type  of  plants. 

Examples  of  Fungi.  The  mushrooms  are  the  largest  fungous 
forms  and  while  some  few  are  edible  the  majority  are  useless  for 
food.  Many  are  poisonous,  and  the  shelf -shaped  mushrooms  found 
on  trees  do  enormous  damage  to  timber.  Just  a  word  of  warning 
at  this  point:  a  "  toad  stool  "  is  merely  a  name  that  some  people 
attach  to  poisonous  mushrooms.  There  is  really  no  such  dif- 
ference. No  "  rule  "  or  "  sign  "  can  be  given  by  which  you  may 
distinguish  poisonous  forms.  Their  food  value  is  very  slight  while 
the  poison  of  the  harmful  forms  is  usually  fatal.  Bearing  this  in 
mind  there  is  but  one  conclusion,  either  learn  to  recognize  one  or 


130 


BIOLOGY  FOR  BEGINNERS 


two  edible  kinds  and  use  them  only,  or  leave  them  all  severely 
alone  as  food. 

Another  class  of  the  fungi  includes  the  rusts  and  smuts  which 
attack  grains,  corn,  and  other  grasses,  doing  enormous  damage 
to  crops.  Mildew  is  a  common  fungus  whose  chief  harm  is  the 
causing  of  rot  in  potato  and  similar  crops,  and  destruction  of  grapes 
and  other  fruits.  Molds  are  also  familiar  forms  which  thrive  upon 


FIG.  42.    Colonies  of  budding  yeast  cells  (Sedgewick  and  Wilson) 
From  Calkins. 


food  stuffs,  bread,  meats,  canned  fruits,  and  even  wood  and  paper, 
if  conditions  are  such  that  their  spores  can  germinate. 

Yeast  plants  are  a  still  simpler  class  of  fungi.  We  use  them  so 
commonly  that  we  hardly  realize  that  they  are  plants  at  all.  Yeast, 
however,  is  a  true  one-celled  plant,  living  on  dilute  sugar  solutions 
which  it  changes  to  alcohol.  It  sets  free  carbon  dioxide  gas  as  a 
waste  product.  Thus  yeast  is  used  in  two  very  different  kinds  of 


SPORE-BEARING  PLANTS  131 

industry,  the  manufacture  of  alcoholic  liquors,  where  the  alcohol 
is  the  desired  product,  and  in  the  making  of  bread,  where  the  car- 
bon dioxide  is  required  to  make  the  loaf  "  light  "  by  its  expansion. 
Yeast  consists  of  single  oval  cells.  It  reproduces  very  rapidly  if 
kept  warm  and  moist  and  supplied  with  sugar  for  food.  Buds 
develop  on  each  parent  cell  and  soon  become  full-sized  cells  which 
again  reproduce,  the  process  being  extremely  rapid.  A  loaf  of 
bread  is  the  product  of  at  least  two  very  different  kinds  of  plants, 
(1)  the  complicated  wheat  plant  whose  store  of  starch  we  make  into 
flour  and  (2)  the  simple  yeast  which  helps  to  make  it  palatable. 

We  have  left  till  the  last  the  most  important  member  of  the 
fungous  group  —  the  bacteria.  They  are  of  such  vast  influence 
both  for  good  and  harm,  that  the  next  chapter  will  be  entirely  de- 
voted to  them. 

COLLATERAL   READING 

Applied  Biology,  Bigelow,  pp.  232-297;  General  Biology',  Sedgwick  and 
Wilson,  pp.  184-191  (yeast);  Practical  Biology,  Smallwood,  pp.  338-375; 
Elementary  Biology,  Peabody  and  Hunt,  pp.  140-153;  Essentials  of  Biology, 
Hunter,  pp.  170-189;  The  Science  of  Plant  Life,  Transeau,  pp.  234-292; 
Plant  Life  and  Plant  Uses,  Coulter,  pp.  360-410;  College  Botany,  Atkinson, 
pp.  137-291. 

SUMMARY 
Plants  in  general. 
Seed  plants. 
Spore  plants.  Examples 

Algae  pond  scums,  sea  weeds,  etc. 

Fungi  mushrooms,  toadstools,  molds 

Lichens  rock  and  bark  patches 

Mosses  common  mosses 

Ferns  common  ferns 

Horse-tails 
Ground-pines 

Fungi  as  typical  spore  plants. 
No  chlorophyll.     Consequence. 
Parasitic  habit: 

Result  to  plant  itself:  degeneration:    dependence. 
Result  to  other  living  organisms: 

1.  Harm  to  hosts 

2.  Destruction  of  food 

3.  Value  as  scavengers 


132  BIOLOGY  FOR   BEGINNERS 

Examples  of  fungi: 

Mushrooms,  some  edible,  cf .  "  toadstools  " 
some  poisonous 
harmful  to  timber,  etc. 
Mildews,  cause  rot  in  potato,  etc. 
Molds,  attack  bread,  meats,  cheese,  etc. 
Yeasts,  structure,  oval  cells 
growth,  by  budding 
conditions  for  growth: 
moisture 
warmth 
food 

food,  sugars 

products,  alcohol  and  carbon  dioxide 
uses,  bread  and  beer 


CHAPTER  XVII 
BACTERIA 

Vocabulary 

Sterilized,  treated  so  as  to  kill  all  germs,  either  by  heat  or  chemicals. 
Culture  medium,  a  substance  prepared  for  growth  of  bacteria. 
Peptone,  soluble  form  of  proteid. 
Inoculation,  intentional  infection  with  germs. 
Immunity,  a  condition  in  which  the  body  is  not  affected  by  bac- 
terial attack. 
Indispensable,  very  necessary. 

Bacteria  are  very  minute,  one-celled,  parasitic  fungous  plants. 
There  are  many  kinds  but  they  are  sometimes  classified  into  three 
groups  according  to  their  shape. 

1.  Coccus  forms  —  round 

2.  Bacillus  forms  —  oblong 

3.  Spirillium  —  spiral  and  curved 

Do  not  forget  that  certain  one -celled,  parasitic  animal  forms  also 
cause  disease  so  that  when  we  speak  of  the  germ  or  microbe,  it  may 
mean  either  a  plant  or  animal  parasite,  but  when  bacteria  are 
mentioned,  only  the  plant  forms  are  included.  Another  point  to 
bear  in  mind  is  that  not  all  bacteria  are  harmful  nor  are  all  infec- 
tious diseases  due  to  bacteria. 

Bacteria  are  very  small,  one  ten  thousandth  to  one  fifty  thou- 
sandth of  an  inch  in  diameter.  Some  are  so  minute  that  they  can 
neither  be  caught  by  a  filter  nor  seen  by  a  microscope. 

Reproduction.  Bacteria,  since  they  have  but  one  cell,  absorb 
food  and  excrete  waste  directly.  Under  favorable  conditions  of 
food  supply,  temperature,  and  moisture,  they  reproduce  with 
enormous  rapidity,  so  that  one  of  these  microscopic  cells  would, 
if  unchecked,  produce  a  mass  of  bacteria  weighing  7000  tons  in 

133 


134 


BIOLOGY  FOR  BEGINNERS 


TYP£S 


TYPE  . 


FIG.  43.    Some  forms  of  useful  and  of  harmful  bacteria.     (Greatly 
enlarged.) 


BACTERIA  135 

three  days.  Fortunately  this  rate  is  never  maintained  because  the 
food  supply  soon  becomes  exhausted,  or  their  own  excreted  waste 
matters  check  their  rapid  growth.  The  tuberculosis  bacterium 
divides  every  thirty  minutes;  compute  the  possible  number  pro- 
duced per  day. 

Occurence.  Bacteria  are  found  almost  everywhere  in  air,  water, 
soil,  food,  inside  plant  and  animal  bodies  whether  dead  or  alive, 
wherever  they  can  find  food  and  suitable  living  conditions.  It  is 
fortunate  that  most  of  this  host  of  one-celled  neighbors  are  either 
harmless  or  useful. 

The  study  of  bacteria  is  called  bacteriology.  It  is  a  science  in 
itself.  The  methods  used  in  its  study  are  interesting. 

Sterilization.  In  the  first  place  all  dishes  and  apparatus  used 
are  sterilized  ;  that  is,  they  are  heated  or  treated  with  chemicals  so 
as  to  kill  any  bacteria  that  might  come  from  the  air  or  water. 

Making  the  "Medium."  Then  a  "culture  medium"  is  made 
from  some  jelly-like  substances  such  as  gelatin  or  agar,  with  which 
beef  extract  or  some  similar  food  is  mixed  and  often  peptone  and 
soda  are  added  to  make  it  easier  for  the  bacteria  to  get  their 
nourishment. 

Inoculation.  This  culture  medium  is  put  in  sterile  dishes  and 
again  sterilized  several  times  by  heat  to  kill  any  bacteria  that 
might  be  present;  the  dishes  are  plugged  with  sterilized  cotton 
which  will  keep  other  bacteria  from  getting  in.  Now  we  are  ready 
for  the  next  step,  called  exposure,  or  inoadation  of  the  cultures. 
This  is  done  by  pouring  upon  the  surface  of  the  culture,  a  small 
amount  of  the  milk  or  water  to  be  tested,  or  by  exposure  to  the  air 
in  the  room  where  the  bacteria  are  to  be  studied.  Touching  with 
the  fingers,  exposure  to  dust,  and  various  other  means  will  permit 
access  of  bacteria  if  any  be  present. 

Growth  of  Cultures.  After  exposure,  the  dishes  are  again  covered 
and  set  in  a  warm  place  for  a  few  hours.  We  know  that  the  culture 
was  sterile,  i.e.,  had  no  bacteria  in  it,  and  we  know  that  conditions 
favorable  to  growth  are  provided.  As  a  result  if  any  bacteria  have 
been  brought  in  contact  with  the  culture  they  soon  multiply  so 
greatly  that  a  spot  or  colony  develops  on  the  gelatin. 


136  BIOLOGY  FOR  BEGINNERS 

Pure  Cultures.  Thus  the  number  and  kind  of  bacteria  to  be 
found  in  the  substance  tested  can  be  determined.  Other  gelatin 
can  be  inoculated  from  some  one  kind  of  colony  forming  a  pure 
culture,  so  that  further  study  can  be  made  and  slides  can  be  pre- 
pared for  use  under  the  miscrocope. 

When  our  mothers  "  put  up  "  canned  fruits  or  vegetables  at 
home,  they  go  through  the  first  part  of  this  same  process.  They 
boil  the  cans,  covers,  and  rubbers,  which  sterilizes  them.  Then 
they  fill  them  while  still  hot  with  the  fruit,  which  has  been  sterilized 
by  cooking;  and  finally  seal  the  cans  to  keep  any  other  bacteria 
from  getting  in  and  causing  the  contents  to  ferment  or  "  work." 

Useful  Forms  of  Bacteria.  Do  not  forget  that  bacteria  do  not 
always  mean  disease,  for  as  a  matter  of  fact,  there  are  many  kinds, 
without  which  we  could  not  live.  If  we  pull  up  a  clover  plant, 
there  are  usually  found  attached  to  its  roots,  numerous  small 
round  bunches,  called  tubercles.  These  are  the  homes  of  millions 
of  bacteria  which  have  the  ability  to  take  the  free  nitrogen  of  the 
air  and  combine  it  into  soil  compounds  which  other  plants  can 
then  use.  These  nitrogen  compounds  are  absolutely  essential  to 
life.  No  other  plant  forms  can  manufacture  them  from  the  air. 
Therefore  we  see  how  important  these  bacteria  are  in  keeping  up 
the  fertility  of  the  soil.  Nitrifying  bacteria  are  found  on  the  roots 
of  all  members  of  the  clover  family,  such  as  peas,  beans,  and  al- 
falfa. It  had  long  been  known  that  plowing  under  a  crop  of  clover 
made  the  soil  better  for  the  other  crops,  but  the  reason  was  not  un- 
derstood till  the  nitrifying  bacteria  were  studied. 

Other  helpful  bacteria  are  those  which,  like  fungi,  aid  in  decay 
and  therefore  act  as  scavengers,  removing  harmful  waste,  and  re- 
turning it  to  the  soil  as  plant  foods.  This  process  is  utilized  in 
sewage  disposal  systems,  where  certain  bacteria  act  on  the  city's 
sewage  —  changing  it  to  an  odorless  and  valuable  fertilizer  instead 
of  a  dangerous  and  expensive  waste  product. 

The  souring  of  milk,  the  making  of  butter  and  cheese,  the 
"  ripening "  of  meats,  and  the  fermentation  of  vinegar,  sauer 
kraut,  and  ensilage,  are  some  food  processes  in  which  bacteria  are 
indispensable.  The  separation  of  hemp  and  flax  fiber  from  the 


BACTERIA  137 

rest  of  the  plant  and  several  steps  in  the  tanning  of  leather,  curing 
tobacco,  and  preparing  sponges,  are  other  processes  which  depend 
on  bacteria. 

Harmfu  Bacteria.  On  the  other  hand,  tuberculosis,  which  causes 
one-seventh  of  all  the  deaths  in  the  world,  is  due  to  the  attack  of 
a  bacterium.  At  least  fifty  per  cent  of  all  deaths  are  due  to  this  and 
other  bacterial  diseases,  of  which  the  following  is  a  partial  list. 

tuberculosis  tooth  decay  anthrax 

erysipelas  pneumonia  cattle  fevers 

leprosy  ptomaine  poisoning  grippe  and  colds 

syphilis  typhoid  fever  lockjaw  (tetanus) 

diphtheria  eye  diseases  cholera 

whooping  cough 

Often  when  bacteria  attack  nitrogenous  foods,  poisonous  sub- 
stances, called  ptomaines,  are  produced.  These  sometimes  cause 
illness  or  death  when  such  food  is  eaten.  Some  serious  plant  diseases 
or  "  blights  "  are  caused  by  bacteria  and  result  in  great  crop  losses. 
Bacteria  were  discovered  by  Pasteur  in  his  reaserches  along  this 
line. 

Defences  against  Bacteria.  With  this  formidable  list  in  view,  it 
is  evident  that  we  ought  to  know  how  to  prevent  these  bacteria 
from  attacking  our  bodies  and  how  to  combat  and  destroy  them 
when  they  obtain  a  foothold  in  our  systems. 

Skin.  Our  first  line  of  defence  against  these  ever-present  enemies 
is  our  skin,  and  the  mucous  membranes  which  line  the  inside  of  the 
body.  If  they  are  clean,  whole,  and  healthy,  few  bacteria  can  get 
inside  our  defences. 

NATURAL  RESISTANCE 

If  they  break  through  this  outer  breastwork,  the  bacteria  have 
to  face  the  second  line  of  defence,  which  is  the  natural  resistance  of 
a  healthy  body  to  any  harmful  invader.  This  second  line  is  de- 
fended by  the  white  corpuscles  in  the  blood,  which  actually  de- 
vour some  of  the  disease  germs,  and  also  by  antitoxins,  which 
overcome  the  poisons  made  by  the  bacteria,  and  which  are  produced 


138  BIOLOGY  FOR  BEGINNERS 

in  the  blood  by  the  presence  of  the  bacteria  themselves.  Thus 
the  attack  tends  to  produce  a  defence  against  itself,  if  the  body 
be  healthy.  This  natural  resistance  to  disease  is  called  natural 
immunity,  and  constantly  protects  us  from  germs  of  whose  pres- 
ence we  are  entirely  unconscious. 

To  provide  conditions  favorable  to  resist  disease  it  is  evident 
then  that  general  good  health  is  essential,  aided  by  cleanliness, 
pure  and  abundant  food,  light,  air,  and  whatever  will  keep  each 
cell  of  our  body  keyed  up  to  repel  the  invader  before  his  rapid  in- 
crease gives  him  the  advantage.  We  know  how  often  when  the 
body  is  "  run  down,"  diseases  are  contracted,  which  would  other- 
wise be  fought  off  without  our  knowing  that  the  bacteria  had 
attacked  us.  How  often  a  "  mere  cold  "  develops  into  some  serious 
ailment,  because  the  cold,  though  perhaps  not  regarded  as  serious, 
lowers  the  resisting  power  of  the  body  and  then  bacteria  find  en- 
trance and  overcome  our  physiological  garrison. 

Defence  by  Antitoxins.  In  case  the  bacteria  do  find  lodgment 
in  our  bodies,  there  is  usually  a  period  of  some  days  between  the 
time  of  exposure  and  the  actual  illness:  this  period  of  incubation 
is  the  time  in  which  the  bacteria  are  overcoming  the  body's  first 
resistance  and  multiplying  sufficiently  to  gain  the  advantage. 
Then  the  colonies  of  bacteria  develop  in  some  organ,  —  as  when 
diphtheria  bacteria  attack  the  throat.  The  throat  is  not  the  only 
portion  harmed,  for  the  bacteria  also  secrete  a  poison  (toxin)  which 
causes  more  serious  trouble  to  other  organs  of  the  body.  If  the 
patient  recovers  it  is  because  his  body  has  been  able  to  gradually 
increase  the  amount  of  antitoxin  in  his  system  and  so  overcome  the 
poisons  produced  by  the  bacteria  which  are  causing  the  disease. 

White  Corpuscles.  The  lymph  glands  in  various  parts  of  the 
body  produce  white  corpuscles,  and  if  the  body  is  in  good  con- 
dition at  the  tune  of  disease  attack,  they  greatly  increase  the  num- 
ber of  these  defenders.  These  corpuscles  are  able  to  actually  "  eat 
up  "  the  bacteria  or  else  carry  them  back  to  the  lymph  glands 
where  they  are  destroyed. 

Opsonins  are  chemical  substances  in  the  blood  whose  function 
is  not  thoroughly  understood,  but  which  have  to  do  with  com- 


BACTERIA  139 

bating  the  attack  of  disease  germs,  by  making  them  more  suscep- 
tible to  the  white  corpuscles.  It  seems  as  if  the  opsonin  in  the  blood 
can  be  increased  by  the  injection  of  dead  germs,  and  this  method 
is  sometimes  used  to  produce  immunity  to  certain  diseases. 

Acquired  Immunity.  In  some  diseases,  it  seems  as  if  the  fact  of 
having  had  the  attack  and  successfully  overcoming  it,  had  provided 
the  body  with  such  ability  to  supply  that  particular  antitoxin 
that  the  person  seldom  has  the  disease  again,  as  for  example  in 
the  case  of  measles  and  whooping-cough.  The  body  has  been 
trained,  as  it  were,  to  oppose  that  kind  of  attack  and  this  is  called 
a  condition  of  "  acquired  immunity." 


ARTIFICIAL  PROTECTION 

Vaccination.  From  this  it  follows  that  if  one  has  a  mild  attack 
of  a  serious  disease,  he  may  develop  sufficient  antitoxin  strength 
to  oppose  the  dangerous  form,  somewhat  as  a  sham  battle  pre- 
pares the  soldier  to  protect  himself  in  the  real  engagement.  This 
fact  is  the  basis  of  vaccination  which  is  the  inoculation  of  a  well 
person  with  a  mild  form  of  smallpox,  by  which  he  becomes  able 
to  resist  the  attack  of  this  terrible  disease.  (Smallpox  is  due  to 
a  one-celled  animal  germ,  not  a  bacterium.)  In  a  similar  way 
protection  is  obtained  against  typhoid  fever  and  hydrophobia. 
Weak  doses  of  the  toxins  of  these  diseases  are  administered,  so 
that  the  body  gradually  increases  its  antitoxin  defences  and  be- 
comes immune  to  fatal  attack.  Some  people  oppose  vaccination 
because  when  improperly  performed,  other  germs  are  introduced 
and  serious  illness  follows  but  this  is  a  very  rare  occurrence.  Be- 
fore vaccination  was  practiced  95  per  cent  of  all  people  had  small- 
pox, thousands  died  and  all  were  scarred  for  life.  Then  it  was 
one  of  the  plagues  of  the  world,  whereas  it  is  now  one  of  the  rarest 
of  diseases. 

Antitoxins.  Another  method  of  helping  our  bodies  to  repel 
germ  attack  is  by  administration  of  the  antitoxin  directly.  In 
vaccination  the  body  learns  to  make  its  own,  but  there  are  cases 
where  a  child  is  too  weak  to  do  this  and  the  actual  antitoxin  is 


140  BIOLOGY  FOR  BEGINNERS 

used.  This  is  especially  true  in  treatment  of  diphtheria.  This 
antitoxin  is  obtained  from  horses,  which  have  acquired  immunity 
by  having  been  inoculated  with  frequent  doses  of  the  diphtheria 
toxin,  till  their  blood  has  an  excess  of  antitoxin,  which  may  then 
be  drawn  off,  prepared  and  injected  into  the  system  of  the  patient 
early  in  the  attack,  thus  supplying  more  antitoxin  than  the  child 
might  be  able  to  produce  in  its  own  cells  even  after  days  of  illness, 
if  at  all. 

Another  dreadful  disease  which  is  successfully  treated  in  this 
way  is  tetanus  or  lockjaw.  This  is  a  frequent  result  of  wounds  in 
which  dirt  gains  entrance,  such  as  Fourth  of  July  pistol  injuries, 
and  cuts  on  the  feet,  which  are  apt  to  be  infected  from  the  soil. 
It  is  not  the  fact  that  the  nail  is  rusty  which  makes  it  dangerous 
to  step  on,  but  that  a  rusty  nail  generally  is  a  dirty  nail,  and  may 
infect  with  disease. 

Germicides.  Other  means  of  destroying  bacteria  are  by  the 
use  of  antiseptics,  and  disinfectants  which  are  chemical  substances 
that  destroy  or  hinder  the  growth  of  disease  germs.  Some  valuable 
antiseptics  which  should  be  used,  even  in  small  wounds,  are  iodine 
hydrogen  peroxide,  alcohol,  ichthyol  ointment,  4  per  cent  solution 
of  carbolic  acid  or  10  per  cent  solution  of  potassium  permanganate. 
Boric  acid,  camphor,  thymol,  and  even  common  salt  are  useful  in 
some  cases. 

Disinfectants  are  chemicals  used  to  kill  germs  outside  the  body, 
as  in  case  of  clothing,  utensils,  bedding,  and  rooms  that  have  been 
occupied  by  persons  ill  with  infectious  diseases.  Bichloride  of 
mercury,  a  dangerous  poison,  is  valuable  for  disinfecting  the  hands 
or  washing  woodwork;  dilute  carbolic  acid  may  be  used  for  the 
hands,  clothing,  or  bedding.  Formaldehyde  solution  may  be  simi- 
larly used,  though  sometimes  injurious  to  the  skin;  several  coal 
tar  products  such  as  cresol,  lysol,  cresoline,  etc.,  are  said  to  be  as 
efficient  as  carbolic  acid,  and  less  dangerous.  For  outdoor  disin- 
fection of  cesspools,  garbage  cans,  or  privies,  chloride  of  lime,  or 
freshly  prepared  milk  of  lime,  may  be  used,  the  former  being  es- 
pecially useful  in  typhoid  fever.  To  disinfect  a  room  following  in- 
fectious disease,  all  woodwork  should  be  thoroughly  scrubbed  with 


BACTERIA  141 

soap  and  water,  walls  re-papered  or  calcimined  if  possible,  bedding 
either  sterilized  or  burned  and  the  room  tightly  closed  and  fumi- 
gated. For  this  purpose  formaldehyde  gas  is  best  and  may  be 
prepared  by  burning  a  formalin  candle,  boiling  a  strong  solution 
of  formalin,  or  by  adding  permanganate  of  potash  crystals  to  the 
solution  in  the  proportion  of  one-half  pound  of  crystals  to  each 
pint  of  formaldehyde.  While  not -so  efficient,  and  also  likely  to 
bleach  colored  furniture,  burning  sulphur  produces  a  gas  which  is 
a  useful  disinfectant.  One  or  the  other  of  these  substances  should 
always  be  used  in  rooms  where  an  infectious  disease  has  occurred. 

Germs,  both  bacteria  and  animal  forms,  are  mostly  killed  at  boil- 
ing temperature.  Drying  checks  their  growth  and  direct  sunlight 
destroys  them  rapidly.  When  we  cook  our  foods,  we  not  only  make 
them  more  digestible  and  attractive,  but  sterilize  them  as  well. 
Milk  may  be  freed  of  the  most  dangerous  bacteria  by  pasteuriza- 
tion, which  means  heating  to  a  temperature  of  from  140  to  150°  F. 
for  a  period  of  30  minutes.  After  pasteurizing  it  must  be  quickly 
cooled  and  kept  closed  and  cool,  or  other  germs  will  find  entrance. 

This  brings  us  to  another  way  in  which  bacteria  do  harm  to  man: 
they  attack  his  foods,  causing  them  to  sour,  ferment,  or  decay. 
Cooking  and  canning  are  two  ways  which  have  been  mentioned 
of  preserving  food  from  bacteria.  Meats  are  protected  by  canning, 
cold  storage,  salting,  smoking,  pickling,  etc. ;  fruits  and  vegetables 
may  be  canned,  dried,  or  pickled  in  vinegar  and  spices  which  are 
really  antiseptics.  Other  more  active  antiseptics  have  been  used 
to  preserve  foods,  such  as  borax,  formalin,  salicylic  acid  and  ben- 
zoate  of  soda,  but,  while  they  kill  the  bacteria,  they  also  harm  the 
person  using  the  foods,  and  so  have  mostly  been  forbidden  by  law. 

Development  of  Bacteriology.  Our  knowledge  of  the  action 
of  bacteria  dates  back  only  about  forty  years,  but  during  this  time 
great  headway  has  been  made  in  their  control.  Pasteur  discovered 
the  relation  of  bacteria  to  fermentation  about  1860  but  it  was  not 
until  1880  that  their  connection  with  human  disease  was  established. 
Pasteur's  great  work  against  rabies  —  mad  dog  poison  —  was 
done  about  1885  and  now  only  one  per  cent  of  the  victims  die, 
instead  of  practically  every  one,  as  formerly.  In  1894  Von  Behring 


142 


BIOLOGY   FOR  BEGINNERS 


and  Roux  developed  the  antitoxin  for  diphtheria.  In  the  United 
States,  deaths  from  this  cause  have  decreased  from  15  to  2  per 
10,000  of  population  —  in  fact  98  per  cent  will  recover  if  treated 
within  two  days.  In  similar  ways  we  are  learning  to  control  ty- 
phoid fever,  tetanus,  influenza,  and  pneumonia.  Our  knowledge 
of  the  means  of  transmission  of  disease  has  led  to  preventive  meas- 
ures even  more  efficient  in  preserving  human  life. 

Another  result  of  modern  investigation  is  the  cheering  fact  that 
no  germ  disease  is  hereditary.  You  may  inherit  low  resistance  to 
germ  attack,  but  if  precautions  are  taken  to  increase  this  resistance 
and  avoid  infection,  you  need  not  suffer  from  the  disease. 


Vaccination 

Anti-toxin  treatment 

Method 

Mild  or  dead  germs  intro- 

Serum of  blood  from  im- 

duced into  body 

mune  animal  introduced 

into  body 

Result 

Body  reacts  and  forms  its 

Anti-toxins  directly  sup- 

own anti-toxins 

plied 

Duration 

Immunity  develops  slow- 

Immunity    provided     at 

ly  but  persists  longer 

once  but  for  only  the 

one  case 

Diseases  treated 

Small-pox 

Diphtheria 

Typhoid  fever 

Tetanus 

Rabies 

Meningitis 

COMPARISON  OF  PASTEURIZING  AND  BOILING  MILK 


Boiling 

Pasteurizing 

Temperature 

212  deg. 

140-150  deg.  (30  min.) 
or 

Effect  on  bacteria 

All  killed,  both  harmful 
and  useful 

160-165  deg.  (  1  min.) 
Most  harmful  ones  killed 
Useful  ones  unharmed 

Effect  on  taste 
Effect  on  food  value 

Changed 
Less  palatable 
Much  reduced 

Unchanged 
Unchanged,    except 

Less  digestible 

vitamines 

BACTERIA 


143 


BACTERIAL  ATTACK  AND  CONTROL 


Point  of  Attack 

Disease  caused 

Means  of  control 

Food 
via  digestive 
organs 

Typhoid 
Cholera 
Dysentery 

Cook  foods,  destroy  flies 
Secure  pure  water  supplies 
Pasteurize  milk,  keep  food  cold 
and  clean 

Air 

via  lungs 

Tuberculosis 
Pneumonia 
Measles,  mumps 

Whooping  cough 

Avoid  dust,  check  "colds" 
Anti-spitting  laws 
Quarantine  laws,  avoid  contact 
with  sick 
Good     food,     sleep,     general 
health 

Skin 
via  wounds 

Blood  poisoning 
Tetanus,  syphilis 

Pus  infections 

Cleanliness 
Use  of  antiseptics  and  disin- 
fectants 
Protect  from  further  bacterial 
attack 

Foods  or  skin 
via  insect  trans- 
mission 

Typhoid 
Malaria 
Yellow  fever 

Destroy  breeding  places 
Drainage 
Cleanliness,  screens,  etc. 
See  Chapter  25  on  "  Insects  and 
Diseases" 

COLLATERAL   READING 

Civic  Biology,  Hunter,  pp.  130-157;  Primer  of  Sanitation,  Ritchie,  entire; 
Story  of  Bacteria,  Prudden,  entire;  Dust  and  Its  Dangers,  Prudden, 
entire;  Drinking  Water  and  Ice,  Prudden,  look  over;  Bacteria  and  Their 
Products,  Woodhead,  pp.  24-47,  75-86;  Our  Secret  Friends  and  Foes, 
Frankland,  look  over;  The  Story  of  Germ  Life,  Conn,  entire;  Bacteria  and 
Daily  Life,  Frankland,  pp.  35-119;  Bacteria  and  Country  Life,  Lipman, 
look  over,  especially  Chap.  2,  5,  6,  7,  13,  17,  34,  41  to  49;  Introduction  to 
Biology,  Bigelow,  pp.  256-279;  Applied  Biology,  Bigelow,  pp.  276-297, 
554-560;  Human  Body  and  Health,  Davidson,  pp.  46-53;  Principles  of 
Health  Control,  Walters,  pp.  218-346;  General  Physiology,  Eddy,  pp.  493- 
503;  Essentials  of  Biology,  Hunter,  pp.  170-183;  The  Human  Mechanism, 
Hough  and  Sedgwick,  pp.  463-504;  Practical  Biology,  Smallwood,  etc., 
pp.  232-258;  Plants  and  their  Uses,  Sargent,  pp.  492-495;  The  Rat  Pest, 
Geographic  Magazine,  July,  1917;  Elementary  Biology,  Peabody  and 
Hunt,  Part  II,  pp.  10-43;  Scientific  Features  of  Modern  Medicine,  Lee,  pp. 
64-79;  High  School  Physiology,  Hewes,  pp.  265-275;  Experiments  in  Plants, 
Osterhout,  pp.  361-408;  Introduction  to  Botany,  Stevens,  pp.  256-263; 
Nature  Study  and  Life,  Hodge,  pp.  457-477;  Practical  Biology,  Smallwood, 


144  BIOLOGY  FOR  BEGINNERS 

pp.  343-353;  Scientific  Features  of  Modern  Medicine,  Lee,  pp.  86-109; 
Community  Hygiene,  Hutchinson,  pp.  233-247;  Handbook  of  Health, 
Hutchinson,  pp.  286-313;  Immune  Sera,  Bolduan  and  Koopman,  look 
through;  Infection  and  Immunity,  Sternberg,  look  through;  General 
Biology,  Sedgwick  and  Wilson,  pp.  192-201;  General  Science,  Caldwell 
and  Eikenberry,  pp.  79-101 

SUMMARY 

Definition:   minute,  one-celled,  parasitic,  fungous  plants. 
Kinds,  coccus  (round);  bacillus  (oblong);  spirillium  (spiral). 

"  Germ  or  microbe"  may  be  either  plant  or  animal  forms. 

"  Bacteria"  applies  only  to  plants. 

Characteristics: 

Size. 

Rate  of  reproduction  (why  limited). 

Favorable  conditions:   food,  moisture,  warmth. 

Occurrence. 

Methods  of  Study. 

1.  Sterilization  of  apparatus  (why  necessary). 

2.  Making  of  "culture  medium"  (a  sterile,  moist  food  supply). 

3.  Inoculation  with  forms  to  be  studied. 

4.  Growth  of  bacterial  "colonies,"  on  the  medium. 

5.  Selection,  and  making  of  "  pure  cultures." 
(Explain  precautions  taken  in  canning  fruits.) 

Useful  forms  of  Bacteria. 

1.  Nitrogen  fixers  on  clover  roots  (why  useful). 

2.  Scavengers  and  decay  producers  (why  useful). 

3.  Forms  necessary  in  following  processes: 

Souring  of  milk,  making  of  cheese. 
Fermentation  of  alcohol,  vinegar,  etc. 
Tanning  leather. 
Preparing  hemp  and  flax. 

Harmful  forms  of  Bacteria. 

(See  list  of  bacterial  disease  in  text.) 

One-half  all  deaths,  one-seventh  by  tuberculosis. 

Those  causing  food  decay.     Plant  blights. 

Natural  defences  against  bacteria,  etc. 

1.  Skin  and  mucous  membranes  (clean,  whole  and  healthy). 

2.  Natural  bodily  resistance,  secured  by 

General  good  health. 
White  corpuscles  (destroy  germs). 
Antitoxins  (oppose  bacterial  poisons). 
Opsonins. 


BACTERIA  145 

Stages  in  bacterial  attack. 

1.  Incubation  (overcoming  bodily  resistance). 

2.  Rapid  growth  of  bacteria. 

3.  Secretion  of  toxins  by  bacteria. 

4.  Secretion  of  antitoxins  by  blood. 

5.  Struggle  between  body  and  bacteria. 

6.  Acquired  immunity  in  some  cases. 

Artificial  Protection. 

1.  Vaccination  (smallpox  and  typhoid). 

Body  resists  mild  attack,  makes  own  antitoxins. 

2.  Antitoxin  treatment  (diphtheria  and  tetanus). 

Antitoxins  developed  in  other  animals  (horse). 
Directly  administered  where  body  is  not  able  to  make  its  own. 
Germicides  (germ  killers). 

Antiseptics  (used  mainly  in  contact  with  body): 
Hydrogen  peroxide  Alcohol 

Carbolic  acid,  4%.  Ichthyol 

Boric  acid  Potassium  permanganate,  10% 

Camphor  Thymol,  salt 

Disinfectants  (used  mainly  outside  the  body): 

Bichloride  of  mercury  furniture,  hands 

Carbolic  acid,  4%  clothing,  hands,  etc. 

Formaldehyde.  rooms,  clothing 

Creosol,  lysol,  etc.  clothing,  etc.,  as  directed 

Chloride  of  lime,  garbage,  refuse,  etc. 

Germs  also  killed  by 

Heat,  as  in  boiling  and  cooking,  pasteurizing 

Sunlight 

Hindered  by  dry  conditions 

Pasteurizing 

Heat  to  140-150  degrees 

Cool  quickly 

Exclude  other  bacteria 

Kills  most  harmful  bacteria,  does  not  change  milk 

To  Disinfect  a  room: 

1.  Clean  all  woodwork  with  soap  and  water 

2.  Refinish  the  walls  if  possible 

3.  Disinfect  furniture  and  bedding  (see  above) 

4.  Fumigate  with 

Formaldehyde 

Formaldehyde  and  potassium  permanganate 

Burning  sulphur  (danger  of  bleaching) 

Development  of  Bacteriology. 

Pasteur,  1860-1880 

Von  Behring,  1894,  diphtheria 

Roux,  1894,  diphtheria 


CHAPTER  XVIII 

PROTOZOA 

Vocabulary 

Protozoa,  "  first  animals,"  that  is,  simplest  in  structure:  one-celled. 
Microscopic,  minute,  so  small  as  to  be  seen  only  with  microscope. 
Fission,  reproduction  by  division  into  two  parts. 
Conjugation,  reproduction  by  union  of  parts  of  the  nucleus. 
Stagnant,  not  flowing,  as  applied  to  water. 
Vacuoles,  bubble-like  cavities  in  protoplasm,  used  in  excretion. 

In  the  study  of  plants  we  have  seen  how  various  forms  start  in 
a  one-celled  stage,  the  egg,  and  develop  into  very  complicated 
forms  with  separate  tissues  of  various  kinds  of  cells.  We  have 
seen  also  that  there  are  plants  so  simple  that  they  never  have 
more  than  one  cell,  in  which  is  performed  all  the  functions  neces- 
sary to  the  plant.  With  animals  the  same  conditions  are  found; 
there  are  the  very  complex  types  such  as  birds,  insects,  and  man 
where  each  function  has  many  sorts  of  cells  (tissues)  concerned  in 
its  performance  —  while  at  the  other  extreme,  there  are  simple 
one-celled  animals,  all  of  whose  life  functions  are  performed  in  their 
single,  microscopic  ceils. 

These  simplest  forms  are  called  the  protozoa  (first  animals)  and 
though  vastly  numerous  and  widely  distributed,  they  are  not 
familiar  because  of  their  small  size.  Small  as  they  are  they  are  very 
important  in  nature,  forming  food  for  higher  animals,  acting  as 
scavengers,  causing  disease  in  a  few  cases,  and  even  forming  layers 
of  the  earth  by  the  deposit  of  their  countless  shells,  as  in  the  case 
of  the  chalk-making  forms. 

Amoeba.  One  of  the  simplest  of  these  simple  animals  is  the 
amoeba  which  lives  in  the  slime  at  the  bottom  of  most  streams 
and  ponds.  Though  barely  visible  to  the  naked  eye,  under  the 

146 


PROTOZOA 


147 


microscope  it  is  seen  to  consist  of  an  irregular  mass  of  jelly-like 
protoplasm  without  even  a  cell  wall,  hence  its  body  (the  one  cell) 
constantly  changes  shape,  with  a  sort  of  flowing  motion.  A  nucleus 
may  be  seen  as  well  as  tiny  particles  of  food  which  are  scattered 
through  the  protoplasm,  and  also  a  bubble-like  cavity  (vacuole) 
which  expands  slowly  and  then  contracts  suddenly,  forcing  out  its 


FIG.  44.  Amoeba  proteus  in  active  moving  condition,  c.v.,  contractile  vacuole; 
f.v.,  food  vacuole;  «,  nucleus;  />,  remains  of  former  pseudopodia.  w.v.,  water 
vacuoles.  The  arrows  indicate  the  direction  of  protoplasmic  flow.  (Sedgewick 
and  Wilson.)  From  Calkins. 

contents.  Simple  as  is  its  structure,  one  learns  to  look  with  re- 
spect and  interest  upon  an  animal  which  with  so  little  material, 
can  yet  perform  all  the  functions  necessary  to  any  organism, 
however  complex. 

The  amoeba  obtains  food  by  extending  lobes  of  its  protoplasm 
and  actually  flowing  around  each  particle.  Digestion  and  as- 


148 


BIOLOGY  FOR  BEGINNERS 


trio*  fnut»*i 


similation  go  on  directly  in  contact  with  the  food,  and  undigested 
particles  are  merely  left  behind  when  it  flows  away  from  them  or 
they  pass  out  through  any  part  of  the  cell.  Oxygen  is  taken  by 
contact  from  the  water  in  which  it  is  dissolved  and  combines 
directly  with  the  food  and  protoplasm  producing  energy,  just  as 
in  all  living  things.  The  contractile  vacuole  acts  as  an  excretory 
organ,  getting  rid  of  waste.  Locomotion  is  secured  by  the  flowing 

of  the  protoplasm,  projec- 
tions being  pushed  out  on 
one  side  and  withdrawn 
on  the  other.  Some  form  of 
sensation  must  be  present 
because  it  responds  to  light, 
food,  moisture,  or  sudden 
jars. 

Reproduction  occurs  as 
soon  as  growth  reaches  a 
certain  size.  The  nucleus 
first  divides  in  two  similar 
portions,  then  the  rest  of 
the  protoplasm  gradually 
separates  in  two  masses, 

each  with  a  nucleus  and  capable  of  independent  life  and  growth. 
This  simple  reproduction  by  mere  division  is  called  fission.  Repro- 
duction by  union  of  anything  like  the  sperm  and  egg  cells  of  plants 
and  other  animals  has  never  been  observed  in  the  amoeba,  though 
it  seems  almost  necessary  that  there  should  be  some  such  process. 
There  are  nearly  a  thousand  close  relatives  of  the  amoeba,  some 
of  which  attach  a  protective  covering  of  tiny  sand  grains  to  their 
body;  others  secrete. a  layer  of  flint  or  lime.  These  shelled  proto- 
zoans are  so  abundant  in  the  tropical  seas  that  they  tinge  the  water 
white  and  their  shells,  falling  to  the  bottom,  make  deposits  of 
limestone,  such  as  the  chalk  cliffs  of  England. 

Paramoecium.  Another  common  protozoan  is  the  paramcecium 
which  is  also  abundant  in  stagnant  water.  We  cultivate  it  in  the 
laboratory  by  putting  some  dry  hay  or  leaves  in  water  and  leaving 


FIG.  45.     Progressive  stages  of  fission 
of  amoeba.    After  Schultz. 


PROTOZOA 


149 


TIHCHOCY6T3 


S  CAHAL9 


them  in  a  warm  place  for  a  few  days.    When  observed  the  liquid 

will  be  found  to  be  swarming  with  various  kinds  of  protozoa,  of 

which  many  are  paramcecia.    Their  appearance  is  due  to  the  fact 

that  most  protozoa  can  live 

in  a  dried  condition  and  so 

are  blown  around  like  dust. 

They  become  attached  to 

the  hay  or  leaves  and  only 

await  moisture  and  warmth 

to  begin  active  life  again. 

This    is    not    reproduction 

but  only  a  resting  stage  to 

carry  them  over  unfavora- 

ble periods. 

Structure.  The  para- 
moecium  has  a  cell  wall 
which  gives  it  a  definite 
oval  shape.  There  is  .also 
a  funnel-shaped  cavity  on 
one  side  which  acts  as  a 
mouth.  The  cell  is  covered 
with  tiny  hair-like  cilia  by 
which  the  paramoecium 
swims  rapidly  and  also  pad- 
dles food  particles  toward 
the  mouth  cavity.  Inside 
the  cell  there  are,  of  course, 
the  protoplasm,  nucleus, 
and  contractile  vacuoles. 
The  latter  are  two  in  num- 
ber and  situated  in  definite 

places  at  the  two  ends  of 

C 


penisrotif 

MOUTH  AHO  QVLLET 


FIG.  46.    Diagram  of  structures  of  Para- 
caildatum  from  an  individual  about 
125  of  an  inch  in  length.     From  Calkins. 


the  cell. 

Specialization.  Now  you  can  understand  that  while  the  para- 
moecium and  amceba  perform  similar  functions,  still,  the  para- 
mcecium  is  much  more  fully  adapted  for  them,  in  so  much  as  it 


150  BIOLOGY  FOR  BEGINNERS 

has  a  fixed  shape;  cilia  for  locomotion  and  food-getting;  a  definite 
mouth  and  gullet,  and  definite  regions  for  excretion.  This  increase 
in  adaptation  of  structure  to  function  is  called  specialization,  or 
division  of  labor,  and  is  the  mark  of  higher  development  in  any 
plant  or  animal. 

Reproduction.  In  paramcecium  this  function  is  more  highly 
developed  than  in  amoeba  and  consists  of  two  processes,  fission 
and  conjugation.  Fission  takes  place,  preceded,  as  usual,  by  the 
division  of  the  nucleus,  and  two  new  individuals  are  produced, 
much  as  in  amoeba,  but  in  a  more  definite  manner.  This  process 
can  go  on  for  only  about  150  times,  when  the  vitality  seems  to  be 
reduced  and  conjugation  takes  place. 

In  conjugation,  two  paramcecia  unite  by  joining  the  region  near 
the  "  mouth  "  cavity,  and  their  cell  wall  becomes  thin  at  the  point 
of  union.  Complicated  divisions  take  place  in  the  nucleus  of  each 
and  finally  a  stage  is  reached  where  there  are  two  parts  to  each 
nucleus,  one  of  which  is  stationary  and  the  other  not.  The  two 
movable  nuclei  now  exchange  places,  passing  through  the  pro- 
toplasm of  the  cells  and  finally  unite  with  the  stationary  nucleus  of 
the  opposite  individual.  After  Jthis  exchange  and  union  of  nuclei 
the  paramcecia  separate  again.  There  has  been  no  gain  in  numbers 
but  the  vitality  of  the  protoplasm  has  been  increased  so  that  re- 
production by  fission  can  go  on  again. 

This  conjugation  does  not  make  more  individuals  as  true 
reproduction  does,  but  it  enables  both  participants  to  repro- 
duce by  fission  and  is  the  first  step  toward  fertilization  in  ani- 
mals, which,  as  in  plants,  is  the  union  of  two  different  cells  from 
two  individuals. 

Parasitic  Protozoans.  Some  protozoans  are  parasitic,  attack- 
ing other  animals  and  producing  serious  diseases,  much  as  do  the 
bacteria.  They  are  often  classified  with  the  latter  as  "  disease 
germs  "  or  "  microbes."  If  we  realize  that  these  terms  include 
both  one-celled  parasitic  plants  (bacteria)  and  one-celled  parasitic 
animals  (protozoa)  then  their  use  is  correct. 

Some  diseases  caused  by  protozoan  parasites  are  in  the  following 
list.  The  way  in  which  they  are  transmitted  will  be  more  fully 
discussed  under  insects  (Chapter  XXV). 


PROTOZOA  151 

malaria  sleeping  sickness  cattle  fever 

smallpox  dysentery  trachoma 

yellow  fever  scarlet  fever  bubonic  plague 

COMPARISON  OF  AMCEBA  AND  PARAMCECIUM 

Amoeba  Paramoecium 


Form 

Variable 

Constant 

Cell  wall 

None 

Present 

Locomotion 

Flowing  lobes 

Cilia 

Speed 

Slow 

Rapid 

Food 
Reproduction 

Absorbed  at  any  point 
Fission 

Definite  region  of  absorption 
Conjugation  and  fission 

COLLATERAL   READING 

Elementary  Text  (Zoology),  Colton,  pp.  286-306;  Elementary  Text 
(Zoology),  Linville  and  Kelley,  pp.  280-291;  Elementary  Text  (Zoology), 
Davenport,  pp.  280-288;  Elementary  Text  (Zoology),  Galloway,  pp.  154-162; 
General  Zoology,  Herrick,  pp.  24-35;  Lessons  in  Zoology,  Needham,  pp.  9- 
21;  Practical  Zoology,  Davison,  pp.  178-184;  Animal  Life.,  Jordan  and 
Kellogg,  pp.  1-50;  Animal  Studies,  Jordan,  Kellogg  &  Heath,  pp.  22-42; 
Animals  and  Man,  Kellogg,  pp.  37-48,  118-123;  Economic  Zoology,  Kellogg 
and  Doane,  pp.  25-47;  Fconomic  Zoology,  Osborne,  pp.  10-35;  Applied 
Biology,  Bigelow,  pp.  300-319;  Biology  Text,  Peabody  and  Hunt,  pp.  164- 
176;  Practical  Biology,  Smallwood,  pp.  45-62;  Life  and  Her  Children, 
Buckley,  pp.  14-32;  Animal  Life,  Thompson,  pp.  210-221;  Life  in  Ponds 
and  Streams,  Furneaux,  pp.  99-113;  Protozoa,  Calkins,  entire1;  Proto- 
Zoology,  Calkins,  entire1;  General  Biology,  Sedgwick  and  Wilson,  pp.  192- 
201. 

See  also  references  on  "Insects  and  Diseases." 
1  Look  through,  note  pictures  especially. 

SUMMARY 

All  living  things  start  in  one-celled  stage. 
Sperm  and  egg  cells  in  higher  forms. 
Bacteria:  one-celled  plants. 
Protozoa:  one-celled  animals. 

Protozoa  (first  animals) : 
1.    Characteristics, 

Minute  size,  numerous,  widely  distributed. 
One-celled,  simple  structure. 


152 


BIOLOGY  FOR  BEGINNERS 


PROTOZOA,     ETC. 


VOLVOX 


KOT  i 


FIG.  47.    Various  types  of  protozoa,  rotifers,  and  other  organisms  often 
found  in  aquarium  cultures.     (Greatly  enlarged.) 


PROTOZOA 


153 


2.    Economic  importance, 

Food,  scavengers,  soil  and  rock  formation. 
Producing  certain  diseases. 
Amoeba  (a  very  simple  protozoan). 

Where  found.  Appearance. 

Structure. 

Protoplasm,  nucleus,  lobes,  vacuoles,  food  grains. 
Paramcecium.     (A  more  specialized  protozoan.) 

Where  found.  Appearance.       How  distributed. 

Structure. 

Protoplasm,  nucleus,  cell  wall,  cilia,  "mouth,"  vacuoles,  food  grains. 
Points  of  advance  over  amoeba: 
Fixed  shape  (cell  wall). 
Cilia  for  locomotion  and  food-getting. 
Definite  mouth  region. 
Two  definite  places  for  excretion. 
Reproduction  both  by  fission  and  conjugation. 


COMPARISON  OF  THE  MEANS  OF  PERFORMING  THE 


Life  Functions 

in  Amoeba 

and  Paramoecium 

Food-getting 
Digestion  and  assimi- 
lation 

By  flowing  lobes 
By  contact  anywhere 

By  cilia 
In  definite  regions 

Oxidation 

Contact  with  dissolved  air 

Same 

Excretion 
Locomotion 
Sensation 

Vacuole,  variable 
Lobes,  variable 
Responds    to    heat,    light, 

Two  vacuoles,  definite 
Cilia,  definite 
Same 

Reproduction 

contact,  moisture,  etc. 
Fission 

Fission  and  conjugation 

Comparison  of  Fission  and  Conjugation 
Fission  (increases  numbers)  Conjugation  (increases  vitality) 


1.  Nucleus  divides. 

2.  Cell  divides. 

3.  Growth  to  adult  size. 


1.  Union  of  two  individuals. 

2.  Complicated  nuclear  division. 

3.  Cross  transfer  of  part  of  nucleus. 

4.  Union  of  portions  of  nuclei. 

5.  Separation  of  individuals. 


CHAPTER  XIX 

METAZOA 

Vocabulary 

Metazoa,  "  animals  further  along,"  that  is,  in  development  and 

specialization,  many-celled  animals. 
Specialization,    development    of    separate    organs    for    different 

functions,  division  of  labor. 
Respective,  separate  or  individual. 
Stimuli,  any  outside  forces  that  affect  plant  or  animal,  such  as 

light,  heat,  contact,  sound,  etc. 

All  one-celled  animals  are  called  protozoa  (first  animals);  all 
those  consisting  of  more  than  one  cell  are  called  metazoa  (animals 
further  along),  meaning  that  they  are  more  complex  in  structure 
and  more  specialized  in  function  than  a  single-celled  animal  can  be. 

Development.  No  matter  how  complicated  a  plant  or  animal 
may  eventually  become,  it  started  in  a  one-celled  stage,  the  fertil- 
ized egg.  This  in  turn  was  the  product  of  the  union  of  the  single 
sperm  cell  with  the  single  ovule  cell.  To  trace  the  development 
from  this  one-celled  stage  to  the  highly  complicated  forms  is  too 
difficult  at  present,  and  forms  the  basis  for  the  whole  science  of 
embryology.  However,  some  of  the  steps  in  the  process  can  be 
briefly  mentioned. 

A  one-celled  animal  (protozoan)  takes  in  food  and  oxygen,  and 
excretes  waste  only  by  means  of  its. exposed  surface.  If  the  di- 
ameter of  a  solid  be  doubled  its  surface  area  is  squared,  but  its 
bulk  is  cubed.  Hence  if  a  protozoan  increased  much  in  size,  it 
would  reach  a  point  where  the  surface  was  too  small  to  provide  for 
the  bulk,  and  it  would  die.  Before  this  point  is  reached,  division 
takes  place  and  growth  begins  again,  up  to  limit  of  size  set  by 
the  ratio  between  surface  and  bulk.  This  is  why  protozoa  are  so 
small  and  why  they  divide  so  frequently.  The  size  which  a  cell 
may  reach  is  therefore  limited  by  the  extent  of  its  surface. 

154 


METAZOA  155 

The  paramoecium  is  much  more  highly  developed  than  the 
amoeba  but  a  -limit  to  its  specialization  and  growth  is  soon  found 
and  a  stage  is  reached  where  further  specialization  in  function  or 
increase  in  size  is  no  longer  possible.  If  further  advance  is  to  be 
obtained,  larger  and  more  complicated  forms  must  develop.  Sup- 
pose that  when  a  protozoan  divides,  the  cells  did  not  separate  but 
remained  attached,  grew,  and  divided  again  and  again.  There 
would  soon  be  produced  a  mass  of  cells  much  larger  than  any  single 
one,  and  with  abundant  surface  exposed  for  food-getting  and 
breathing.  In  such  an  animal  the  outer  cells  could  best  attend  to 
locomotion,  sensation,  and  food-getting,  while  the  inner  cells 
could  carry  on  digestion  and  reproduction.  Pandorina  and  other 
simple  metazoans  represent  this  stage. 

If  a  solid  mass  of  cells  continued  to  enlarge,  the  innermost  ones 
would  be  so  far  from  contact  with  food  and  air  that  a  limit  in  size 
of  the  mass  would  be  reached,  just  as  with  the  single  cell.  To 
meet  this  condition,  the  next  higher  forms  consist  of  hollow  spheres 
of  cells,  thus  giving  an  inner  and  outer  surface,  and  permitting 
much  larger  and  more  complicated  forms.  Volvox  is  a  representa- 
tive of  this  condition.  It  consists  of  thousands  of  cells,  is  large 
enough  to  be  visible  to  the  eye,  and  has  very  highly  developed 
reproductive  and  locomotor  cells. 

A  hollow  sphere  cannot  increase  indefinitely  in  size  as  the  single 
cell  layer  would  not  be  strong  enough,  so  in  the  next  higher  forms 
an  infolding  of  the  wall  takes  place,  much  as  a  hollow  rubber  ball 
can  be  squeezed  into  a  cup-shaped  form.  Its  walls  will  now  be 
double  with  a  space  between  them,  in  which  a  third  cell  layer  de- 
velops. This  three-layered  stage  is  reached  in  the  simplest  sponges, 
and  from  the  three  layers  develop  all  the  tissues  of  higher 
forms. 

It  is  important  to  remember  that  every  plant  and  animal  began 
life  as  a  single  cell,  the  fertilized  egg.  This  by  repeated  divisions 
passed  through  the  stages  just  described,  developed  from  a  mass 
of  unspecialized  cells  into  higher  forms  with  tissues  and  organs. 
Finally  it  reaches  its  destined  stopping  place  whether  in  the  simple 
volvox  or  the  complicated  insect,  bird,  or  man. 


156  BIOLOGY  FOR  BEGINNERS 

Specialization.  Robinson  Crusoe  on  his  desert  island  had  to 
perform  all  the  processes  needed  to  supply  his  wants.  He  had  to 
catch  and  prepare  his  food,  make  his  clothes  and  shoes,  build  his 
house  and  defend  himself  against  enemies.  Even  though  he  be- 
came somewhat  skillful  at  all  these  duties  he  could  never  hope 
to  excel  in  any.  He  was,  in  fact,  in  the  position  of  the  protozoan 
where  all  the  life  functions  are  performed  by  one  cell.  Even  though 
that  cell  be  highly  developed  as  in  paramoecium  or  vorticella,  still 
its  limit  of  advance  is  soon  reached. 

Now,  if  there  had  been  ten  men  shipwrecked  with  Crusoe,  it 
would  have  been  possible  for  one  to  get  food,  another  to  prepare 
it,  others  to  build  houses  and  so  on.  The  increase  in  numbers  per- 
mitted division  of  labor.  This  is  precisely  the  case  with  such  forms 
as  volvox  and  all  higher  types;  the  increase  in  the  number  of  their 
cells  makes  possible  a  separation  of  life  functions,  which  is  actually 
division  of  labor  among  cells. 

To  return  to  the  desert  island  again,  if  one  man  continued  mak- 
ing shoes  or  another  did  all  the  building,  each  would  soon  acquire 
skill  and  perform  his  duty  better;  he  would  have  become  a  special- 
ist in  his  line.  Cells  also  are  able  to  perform  their  functions  better 
and  better  by  constant  use.  Specialization  is  the  term  applied  to 
this  condition  in  cells  as  well  as  in  men. 

Finally,  both  cells  and  men  would  acquire  special  fitness  for 
their  tasks.  This  special  fitness  is  called  adaptation  and  is 
the  permanent  result  of  specialization.  The  more  perfectly  a 
plant  or  animal  is  adapted  to  its  environment,  the  better  is 
its  chance  to  survive;  hence  this  matter  of  development, 
division  of  labor,  specialization,  and  adaptation  is  of  the  utmost 
importance. 

Interdependence.  There  is,  however,  another  phase  of  this  mat- 
ter of  specialization,  which  cannot  be  overlooked.  The  man  who 
devotes  himself  solely  to  the  making  of  shoes,  loses  the  ability  to 
do  many  other  necessary  things.  Cells  and  tissues  which  become 
adapted  for  special  functions  are  all  the  more  dependent  upon  other 
specialized  cells  for  equally  important  services.  So  it  comes  to 
pass  that  the  more  highly  specialized  a  plant  or  animal  becomes 


METAZOA  157 

the  more  each  part  depends  upon  all  the  others,  and  the  more  dif- 
ficult it  is  to  replace  or  to  do  without  a  damaged  tissue  or  organ. 
A  simple  protozoan  can  be  divided  and  each  half  perform  all  the 
vital  functions.  Needless  to  say  this  cannot  be  done  with  higher 
specialized  forms  like  the  insect  or  bird,  in  which  the  interdepen- 
dence has  developed  to  a  considerable  degree. 

By    increase    in    numbers 
Division    of    Labor    is    made    possible, 

by     which 

Workmen"*  "    ^  Col  1st 

gain.  tfafn 

Adaptation 


for 

Business 

called  called 

SPECIALIZATION 


FIG.  48.     Chart  showing  evolution  of  specialization. 

Forms  of  Metazoans.  The  sponges  have  their  division  of  labor 
confined  to  specialization  of  separate  cells  for  various  functions. 
The  next  higher  group  (ccelenterates)  which  includes  the  hydra, 
coral  polyps,  sea  anemone,  and  jellyfish,  have  cells  performing 
similar  functions  grouped  together  in  true  tissues. 

The  next  group  (true  worms),  such  as  the  earthworm,  carry  this 
division  of  labor  still  farther,  having  special  digestive,  circulatory, 
and  excretory  organs,  of  complicated  structure,  and  a  true  nervous 
system  with  perhaps  the  beginning  of  a  brain. 

Still  more  complicated  in  structure  and  specialized  in  function 
are  the  molluscs  which  include  clams,  oysters,  snails,  squids,  and 
devil  fish.  These  have  very  complicated  gills  for  breathing,  heart 
and  circulatory  system  much  more  developed,  muscular  and 


158  BIOLOGY  FOR  BEGINNERS 

nervous  systems  becoming  very  efficient.  In  some  there  are  found 
eyes  and  other  sense  organs. 

The  arthropods,  which  include  the  lobster  and  crab,  all  insects, 
and  spiders,  constitute  an  enormous  and  highly  specialized  group 
whose  adaptations  we  shall  study  in  detail.  Then  at  the  top  of  the 
list  come  the  vertebrates,  including  all  backboned  animals,  fish, 
frog,  snake,  bird,  cat,  and  man  whose  place  at  the  head  of  the  class 
is  due,  as  always,  to  the  specialization  and  development  of  the 
organ  with  the  highest  function,  namely  the  brain,  with  its  ability 
to  think  and  reason. 

All  this  increase  in  adaptation  brings  the  animal  in  closer  touch 
with  its  surroundings  or  environment.  The  amoeba  vaguely  turns 
toward  food  and  moisture,  contracts  if  disturbed  or  perhaps  turns 
away  from  strong  light.  As  development  progresses,  response  is 
made  to  other  outside  forces  (stimuli)  and  we  have  organs  for 
touch,  taste,  smell,  hearing,  and  sight,  all  of  which  enable  the 
animal  to  adapt  its  life  to  its  environment  and  by  that  means  be- 
come successful  in  the  struggle  for  existence  which  goes  on  with 
its  neighbors. 

COLLATERAL   READING 

General  Zoology,  Linville  and  Kelly,  pp.  292-304;  Animal  Life,  Jordan 
and  Kellogg,  pp.  24-49;  Animal  Studies,  Jordan,  Kellogg  and  Heath, 
pp.  33-42;  Animal  Life,  Thompson,  pp.  143-152;  Comparative  Zoology, 
Kingsley,  pp.  318-320;  Elementary  Zoology,  Kellogg,  pp.  57-63;  Essentials 
of  Biology,  Hunter,  pp.  199-210. 


SUMMARY 

Protozoa  (first  animals),  one  celled. 
Metazoa  (animals  further  on),  more  than  one  celled. 
1.    Development. 

Plant  and  animal  begin  as  single  cells  (sperm,  ovule). 
Stages  of  progress. 
One  cell. 

Two  cells  to  many  in  mass  (Pandorina). 
Hollow  mass  of  cells  (Volvox). 
In-folded,  hollow  form,  three  layers  (Sponges). 
All  higher  forms,  tissues  from  these  layers. 


METAZOA  159 

COMPARISON  OF  PROTOZOA  AND  METAZOA 


Protozoa 

Metazoa 

One-celled 

No  specialization  in  simplest  except 

the  nucleus 
Some  have  a  cell  wall,  cilia, "  mouth  " 

but  no  regular  systems  of  organs 
Reproduce  by  fission  or  conjugation 
Excretion  by  vacuoles 

Minute  size 

No  "body  wall"  either  in  embryo  or 
adult 


Many  celled 

Specialized  tissues  and  organs 

Digestive,  respiratory  and  nervous  sys- 
tems 

Reproduce  by  eggs  and  sperms 

Excretion  by  kidneys,  or  analogous  or- 
gans, skin,  and  lungs 

Much  larger  size 

Three  layers  in  embryonic  body  wall 
which  develop  as  follows: 

1.  Ectoderm,  forms  outer  skin  and  its 

appendages :  —  Nervous  system 
and  sense  organs 

2.  Mesoderm,    forms   inner   skin,   fat, 

bone,  muscle,  connective  tissue, 
serous  membranes 

3.  Endoderm,     forms    mucous    mem- 

branes and  all  organs  that  it 
lines,  gills,  lungs,  glands 


Classes  of 
Metazoans 

Degree  of  Specialization 

Representative 

1.   Sponges 

Cells  adapted  for  food  getting,  di- 
gestion and  reproduction 

Bath  sponge 

2.    Coelenterates 

Tissues  for  the  above  processes  and 
for  locomotion 

Hydra 
Jelly  fish 

3.   Worms 

Organs  well  developed,  nerves,  blood 
vessels,  muscles 

Earthworm 

4.   Molluscs 

Sense  organs,  gills,  heart,  etc.  more 
complicated 

Snail 
Clam 

5.   Arthropods 

Great  specialization,  skeleton,  all 
senses,  very  active,  nervous  sys- 
tem and  instinct 

Insects 
Crayfish 
Spiders 

6.   Vertebrates 

Great  internal  specialization,  high 
special  senses,  brain,  instinct,  and 
reason,  varied  locomotion,  skeleton 

Fish 
Frogs 
Reptiles 
Birds 
Man 

160  BIOLOGY  FOR  BEGINNERS 

2.  Specialization. 

Beginning  as  single  cell. 

Increase  in  number  of  cells. 

Separation  of  functions  (division  of  labor). 

Better  performance  of  functions  (specialization). 

Development  of  fitness  for  functions  (adaptation). 

3.  Interdependence. 

1.  Advance  in  development  means  advance  in  adaptation. 

2.  Advance    in    adaptation    means    closer    contact    with    sur- 

roundings. 

3.  Both  of  which  mean  success  in  the  struggle  for  existence. 


CHAPTER  XX 

WORMS 

Vocabulary 

Anterior,  the  end  toward  the  head,  usually  the  end  that  precedes 

in  locomotion. 

Posterior,  the  end  farthest  from  the  head. 
Analogous,  having  similar  function. 
Homologous,  having  similar  structure  or  origin. 
Setae,  hair-like  projections  by  which  some  worms  travel. 
Incalculable,  impossible  to  estimate. 
Degeneration,  loss  of  ability  to  perform  function,  loss  of  structures 

due  to  disuse. 

The  worms  may  be  taken  as  a  class  of  animals  showing  a  mod- 
erate degree  of  specialization.  They  include  the  common  earth- 
worm, leeches,  bloodsuckers,  tapeworms,  horsehair  worms,  etc. 

THE  EARTHWORM 

External  Features.  The  earthworm  is  familiar  and  will  do  to 
represent  the  group.  Its  slender  body  is  divided  into  rings  or  seg- 
ments. The  larger  end,  near  which  is  a  light  colored  girdle,  is  the 
head  (anterior)  end;  while  the  vent,  or  opening  of  the  intestine 
marks  the  opposite  (posterior)  extremity.  Projecting  from  each 
segment  are  four  pairs  of  bristles  (setae)  which  are  operated  by 
separate  muscles  and  are  used  in  locomotion.  The  girdle  secretes 
the  case  in  which  the  eggs  are  deposited  and  near  it  are  the  tiny 
openings  of  the  egg  and  sperm  ducts,  since  the  organs  of  both 
sexes  are  found  in  the  same  animal.  On  opening  the  body,  the  wall 
is  found  to  consist  of  a  very  thin  cuticle  and  two  thick  layers  of 
muscle,  one  running  lengthwise,  and  the  other  around  the  body. 

Digestive  System.  Inside  the  body  wall,  the  large  digestive 
system  can  easily  be  recognized,  there  being  a  muscular  pharynx,  a 

161 


162  BIOLOGY  FOR  BEGINNERS 

crop,  stomach,  and  long,  straight  intestine,  terminating  at  the  vent. 

Circulatory  System.  Not  so  conspicuous  is  the  circulatory 
system,  which  consists  of  two  large  blood  vessels,  one  above,  the 
other  below,  the  digestive  tract,  connected  by  branches  in  each 
segment.  Some  of  these  branches  pulsate,  acting  as  a  heart,  to 
drive  the  blood  through  the  system.  It  must  be  remembered  that 
the  functions  of  any  circulatory  system  are  ones  of  transportation. 
It  carries  food  from  the  digestive  organs  to  the  tissues,  oxygen 
from  the  breathing  organs  to  the  tissues,  and  waste  products  from 
tissues  to  the  organs  of  excretion.  In  all  animals  less  specialized 
than  the  worm,  the  structure  was  so  simple  that  these  processes 
were  carried  on  directly  by  osmosis,  but  in  the  worm,  division  of 
labor  is  more  complete,  the  various  tissues  more  complicated  and 
so,  for  the  first  time,  a  transportation  system  is  developed. 

Excretory  and  Nervous  Systems.  Besides  the  circulatory  organs, 
there  are  rather  complicated  sets  of  tubes  in  each  segment,  which 
excrete  waste  matter.  There  are  two  sets  of  reproductive  glands 
between  the  pharynx  and  stomach.  On  the  lower  (ventral)  side 
of  the  body  is  a  double  row  of  light-colored  threads  (the  nervous 
system),  united  in  each  segment,  and  ending  in  a  tiny  knob  near 
the  mouth,  which  corresponds  somewhat  to  the  brain.  When 
such  an-  animal  is  compared  with  the  paramoecium,  it  is  evident 
that  its  functions  have  much  better  machinery  for  their  perform- 
ance. 

Locomotion.  The  worm  is  adapted  for  locomotion  by  the  body 
muscles  and  setae.  The  muscles  extend  the  anterior  part  of  the 
body,  the  setae  are  slanted  backward  and  grip  the  soil,  and  the 
posterior  part  of  the  body  is  pulled  forward  with  a  sort  of  wave- 
like  motion.  By  this  means  the  worm  travels  on  the  surface  or 
burrows  in  the  ground.  Burrowing  is  assisted  by  the  fact  that  the 
earthworm  practically  eats  its  way,  taking  the  soil  into  its  digestive 
tract,  absorbing  what  organic  matter  it  can  use  as  food,  and  bring- 
ing the  unused  earth  to  the  surface  as  "  worm  castings."  These 
are  often  seen  on  lawns,  tennis  courts,  and  golf  greens. 

Analogous  Organs.  Organs  in  different  animals  which  perform 
similar  functions  are  called  analogous  organs.  The  setae  and 


WORMS 


163 


retractor  and  protractor 
muscles  of  the  pharynx,.. 

cesophageal  pouches- 
seminal  receptacles' 
seminal 


cerebral  ganglion 

pharynx 
iphagus 


FIG.  49.    Dissection  of  the  earthworm,  Lumbricus  sp.     From  Kellogg. 


164 


BIOLOGY   FOR  BEGINNERS 


muscles  of  the  worm  are  analogous  to  the  cilia  of  the  paramcecium, 
or  the  flowing  lobes  of  the  amoeba.  (What  analogous  organs  in 
fish,  bird,  and  man?) 

PARASITIC          WORMS 


TAPE    WORM 


HEAP 


10    IN 


FIG.  50.    Diagram  showing  structure  of  tapeworm. 

Food.  The  food  of  the  earthworm  consists  of  leaves  of  cabbage, 
celery,  and  other  plants,  as  well  as  some  kinds  of  meat,  together 
with  organic  matter  found  in  the  soil.  This  is  gathered  at  night, 


WORMS 


165 


taken  into  the  burrows  and  eaten,  while  the  waste  is  brought  to 
the  surface  with  the  earth  as  castings. 

Economic  Value.  This  method  of  feeding  loosens  and  enriches 
the  soil,  performing  about  the  same  work  as  does  the  farmers' 
plow,  though  to  a  greater  extent,  for  the  worms  are  found  in  all 
parts  of  the  world,  in  such  numbers  that  they  pass  through  their 


HOST 


FIG.  51.  Life  history  of  beef  tapeworm.  A,  adult  tapeworm  in  intestine  of 
man;  B,  proglottid  full  of  eggs  on  ground;  C,  eggs  on  ground;  D,  six-hooked 
larva  (onchopore)  set  free  and  bores  through  tissues  of  cow;  E,  cysticercus 
or  bladderworm,  hi  cow's  flesh;  F,  young  tapeworm  in  man.  From  Pearse. 


bodies  an  average  of  ten  tons  of  soil  per  acre,  every  year,  and  thus 
do  an  incalculable  service  to  the  farmer.  Thus  the  humble  earth- 
worm, whose  function  may  have  seemed  to  be  to  furnish  bait  for 
fishing,  now  is  seen  to  be  a  very  useful  member  of  society.  It 
has,  however,  some  very  bad  relatives,  which  do  a  great  deal  of 
harm  and  therefore  require  special  mention. 


166 


BIOLOGY  FOR  BEGINNERS 


PARASITIC  WORMS 

In  this  group  are  included  the  tapeworm,  trichina,  hookworm, 
and  many  others.    As  is  often  the  case,  they  are  harmful  because 
parasitic.    A  parasite,  as  has  been  said, 
takes  the  nourishment  of  another  creature 
instead  of  getting  its  own. 

Tapeworm.  The  tapeworm  lives  first 
within  the  body  of  pigs  or  cattle,  the  egg 
being  taken  in  with  their  food.  It  develops 
in  the  intestine,  bores  its  way  into  the 
muscles  and  goes  into  a  resting  stage. 
If  the  flesh  of  such  animals  be  eaten  when 
not  thoroughly  cooked  the  development 
continues  in  the  intestine  of  man,  where 
the  worm  attaches  itself  by  hooks  on  its 
head,  lives  on  the  digested  food  with  which 
it  is  surrounded  and  by  robbing  its  host  of 
needed  nourishment,  produces  segment  after  segment  till  a  length  of 
thirty  to  fifty  feet  may  be  attained.  These  segments  are  practically 


FIG.  52.  Encapsuled 
trichinae  in  trunk  muscle 
of  pig.  (Greatly  magni- 
fied, after  Braun.)  From 
Kellogg  and  Doane. 


FIG.  53.    Hookworm,  Necator  americanus.    a,  Male;    b,  female.     (Greatly 
enlarged;   after  Wilder.)     From  Kellogg  and  Doane. 

sacs  of  eggs  which  break  off  from  time  to  time,  allowing  the  eggs 
to  escape,  dry,  and  scatter,  where  hogs  or  other  animals  may  eat 
them  and  start  the  circle  over. 


WORMS 


167 


Trichina.  Round  worms  are  another  class  of  parasites,  of  which 
the  "  vinegar  eel  "  and  the  intestinal  pin  worms  are  comparatively 
harmless  forms.  The  pork  worm  (trichina)  of  this  same  class  may 
cause  serious  illness  or  death.  These  worms  pass  their  first  stage 
in  the  pig,  dog,  cat,  ox,  or  horse,  where  they  bore  into  the  muscles, 
surround  themselves  with  a  coating  (cyst),  and  remain  alive  but 
inactive.  If  such  flesh  be  eaten  when  improperly  cooked  the  cyst 
is  dissolved,  the  worms  develop, 
bore  through  the  tissues 
again,  and  produce  the  painful 
and  often  fatal  disease  known 
as  trichinosis.  The  tapeworm 
is  large;  usually  only  one  is 
present  and  it  does  its  chief 
harm  by  absorbing  food 
needed  to  nourish  the  body. 
The  trichina,  on  the  other 
hand,  is  microscopic  in  size, 
vastly  numerous,  and  pro- 
duces acute  disease  by  penetra- 
tion of  the  tissues.  Careful  in- 
spection and  thorough  cooking 


Fig.  54.  Section  through  the  skin 
of  a  dog  two  hours  after  it  has  been 
infected  with  the  Old  World  hook- 
worm. (Greatly  enlarged;  after 
Wilder.)  From  Kellogg  and  Doane. 


of  meats  are  lessons  to  be  learned 
from  the  above  life  histories. 

Hookworm.  The  hookworm  is  another  parasite,  found  in  the 
southern  states,  which  attacks  man  by  way  of  the  feet  and  thence 
by  way  of  the  veins,  lungs,  and  throat,  penetrates  to  the  intestine, 
where  it  absorbs  food  and  causes  loss  of  blood.  This  lowers  its 
victim's  strength  and  produces  the  characteristic  laziness  of  the 
"  poor  whites  "  of  the  South.  Almost  all  animals,  from  clams  and 
insects  to  cattle  and  man,  are  subject  to  the  attacks  of  parasitic 
worms.  The  hookworm  alone  costs  this  country  about  twenty 
million  dollars  ($20,000,000)  per  year,  in  loss  of  labor  due  to  its 
effect  on  health. 

Note:  The  "  horsehair  snake  "  which  you  frequently  find  in 
ponds  and  streams  has  nothing  to  do  with  a  horsehair,  nor  is  it  a 


168 


BIOLOGY  FOR  BEGINNERS 


II 
II 


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IB 


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WORMS  169 

snake.  It  is  one  of  the  round  worms  (related  to  the  "  vinegar 
eel  "  which  is  also  not  an  eel)  and  is  parasitic  upon  beetles,  grass- 
hoppers, and  other  insects,  thus  doing  considerable  good. 

COLLATERAL   READING 

Vegetable  Mould  and  Earthworms,  Darwin,  entire;  Life  and  Her  Chil- 
dren, Buckley,  pp.  135-152;  Economic  Zoology,  Osborne,  pp.  67-120; 
Economic  Zoology,  Kellogg  and  Doane,  pp.  98-105;  Elementary  Text,  Lin- 
ville  and  Kelly,  pp.  195-235;  Practical  Zoology,  Davison,  pp.  150-161: 
Applied  Biology,  Bigelow,  pp.  340-354;  Animal  Studies,  Jordan,  Kellogg 
and  Heath,  pp.  59-88;  Life  in  Ponds  and  Streams,  Furneaux,  pp.  114-126. 

See  also  articles  under  "Worms,"  "Tapeworm,"  "Trichina,"  "Leech" 
in  encyclopedias. 

SUMMARY 

Representatives. 

Earthworm,  tapeworm,  hairworm,    vinegar  eel,  leech,  etc.  (not  cater- 
pillars). 

anterior  and  posterior  (define  in  notes), 
dorsal  and  ventral  (define  in  notes). 

External  Structure.     Shape. 

Segments,  count  them  as  far  as  girdle. 
Girdle,  function. 

Mouth,  call  attention  to  pre-oral  lobe.     Vent. 
Setae,  adaptations. 

1.  Number. 

2.  Location  on  sides. 

3.  Attached  muscles. 

Functions  of  Setae. 

1.  Locomotion,  2.  burrowing,  3.  food-getting. 
Reproductive  openings  on  segments  9,  10  and  14,  15. 
Both  sexes  in  individual. 

Internal  Structure. 

Body  wall,  two  muscle  layers,  use  of  each.     Cuticle. 
(Lack  of  skeleton  and  consequent  slow  motion.) 
Digestive  system. 

Mouth,  manner  of  food-getting. 

Muscular  pharynx,  function. 

Crop,  stomach,  and  intestine  with  special  functions. 

(Glands  and  schemes  for  increase  of  digestive  area.) 
Circulatory  system. 

Dorsal  and  ventral  vessels. 

Cross  tubes  in  each  segment,  some  pulsate. 


170  BIOLOGY  FOR  BEGINNERS 

Functions  of  any  circulatory  system. 

Transfer  of  food  from  digestive  organs  to  tissues. 
Transfer  of  oxygen  from  lungs  to  tissues. 
Transfer  of  waste  from  tissues  to  excretive  organs. 
Excretory  organs. 

Pair  in  each  segment,  well  developed. 
Nervous  system. 

Simple  "  brain  "  and  ventral  nerve  chain. 

Separate  nerve  branches,  much  higher  than  previous  animals  studied. 

Locomotion: 

Adaptations  for, 

1.  Body  muscles,  two  layers,  different  motions. 

2.  Setae  with  their  own  muscles. 

3.  Habit  of  flattening  the  "  tail  "  region  in  burrow. 

Burrowing: 

Adaptations  for, 

1.  As  above. 

2.  Habit  of  swallowing  earth  through  which  it  goes. 

3.  Evidence  shown  in  "castings." 

Food-getting : 

Food,  celery,  lettuce,  meat,  etc.,  from  surface,  ta^en  below;    organic 

matter  in  soil, 
(manner  of  eating;  use  of  pharynx  and  air  pressure). 

Economic  value: 

Earthworm,  loosens  and  enriches  soil,  brings  up  fresh  earth, 
takes  down  organic  matter,  10  tons  per  acre  per  year. 

Reasons  for  development  of  circulatory  system  in  higher  forms. 
More  numerous  cells. 
Greater  division  of  labor. 

All  tissues  not  in  reach  of  food  or  air  by  mere  osmosis. 
Need  for  transportation  system. 

Analogous  organs: 
Definition. 

Examples:  setae,  cilia,  pseudopodia,  all  for  locomotion, 
similar  examples  from  fish,  bird,  man,  etc. 

Parasitism. 

Results: 

Harm  or  death  to  host. 

Degeneration. 

Loss  of  organs.  . 


Absolute  dependence. 
Need  for  vast  reproduction. 


to  parasite. 


WORMS  171 

Tapeworm. 

1.  Eggs  eaten  by  pigs  or  cattle. 

2.  Egg  develops  in  intestine. 

3.  Young  bore  into  muscles,  and  go  into  resting  stage. 

4.  Meat  eaten  by  man  (not  thoroughly  cooked). 

5.  Development  continues.     Causes  weakness  and  anaemia. 

6.  Head  attaches  by  hooks,  absorbs  food,  grows  by  segments. 

7.  Segments  produce  many  eggs,  which  are  scattered. 

Trichina  (related  to  vinegar  worms,  and  intestinal  worms) : 

1.  Young 'bore  into  muscles  and  form  cysts  (in  animals). 

2.  Uncooked  flesh  eaten  and  cyst  dissolves  (in  man). 

3.  Young  again  bore  into  muscles  producing  disease,  cr  death. 

Hookworm. 

1.  Enters  by  way  of  feet,  veins,  lungs,  throat,  intestine. 

2.  Punctures  intestines,  causing  loss  of  blood  and  absorbs  food. 

3.  Lowers  strength,  makes  susceptible  to  other  diseases. 

4.  Loss  in  labor  of  $20,000,000  per  year  in  U.  S. 

Explain: 

"  Horse  hair  snakes." 

Vinegar  "  eels." 
"  Raining  down  "  of  earthworms. 


CHAPTER  XXI 

ARTHROPODS 

Vocabulary 

Segmented,  made  up  of  joints  or  sections. 

Dorsal,  the  region  of  the  back,  usually,  but  not  always,  uppermost 

in  animals. 
Ventral,  the  side  opposite  the  dorsal,  the  region  of  the  belly,  usually 

underneath. 
Genus,  next  to  the  smallest  general  division  in  classification; 

plural  is  genera. 
Species,  the  smallest  general  division  in  classification;    plural 

is  also  species  (specie  means  money). 

The  group  of  animals  next  to  be  studied  is  called  the  arthropods 
(jointed  foot)  because  all  their  leg-like  appendages  are  divided  in 
joints  or  segments. 

Characteristics.  They  are  the  largest  group  of  living  things  in 
the  world,  outnumbering  all  the  other  species  of  the  animal  king- 
dom. These  numerous  forms  all  agree  in  the  following  points: 

1.  They  have  jointed  appendages. 

2.  They  have  an  external  skeleton. 

3.  The  body  is  segmented  and  consists  of  three  regions, 

(a)  head  specialized  for  food-getting  and  sensation. 

(b)  thorax  for  locomotion. 

(c)  abdomen  not  highly  specialized. 

4.  Heart  is  in  the  back  (dorsal)  region. 

5.  Nervous  system  is  beneath  (ventral). 

Classes.  The  arthropods  are  divided  into  three  or  sometimes 
four  classes,  the  fourth  being  rather  indefinite,  and  including  the 
worm-like  forms  such  as  the  centipedes  and  "  thousand  legs." 

1.  Crustacea,  which  include  crayfish,  lobster,  crab,  shrimp,  and 
many  others. 

172  ' 


ARTHROPODS  173 

2.  Accra ta,  the  spiders 

3.  Insecta,  the  insects. 

4.  Myriapods,  worm-like  forms. 

The  members  of  each  of  these  classes  have  all  the  characteristics 
of  the  arthropods,  but  there  are  additional  points  of  resemblance 
within  each  class.  For  instance,  all  the  Crustacea  have  the  head 
and  thorax  united  into  a  cephalothorax  (head-thorax)  which  is 
covered  by  a  part  of  the  external  skeleton 
called  the  carapace.  Usually  they  have 
five  pairs  of  legs  and  breathe  by  gills 
attached  to  them. 

The  acerata  (spiders)  have  no  carapace, 
have  four  pairs  of  legs  and  breathe  by  air 
sacs  or  tracheae.  The  insects'  head  and 
thorax  are  separate;  they  have  three  pairs 
of  legs  and  usually  wings  as  well,  and 
breathe  by  means  of  tracheae.  (For 
further  comparison  see  tabulation.) 

Classification.  Each  of  these  three 
classes  is  further  divided  into  groups  called 
orders,  the  orders  into  families,  and  the 
families  into  still  smaller  groups  called 
genera  (singular:  genus)  and  genera  into 
species  (singular:  species  also). 

As  we  come  down  in  the  classification, 
the  groups  have  more  and  more  points  of 
resemblance,  but  of  course  include  fewer 
individuals.  Take,  for  instance,  the  com- 
mon grasshopper;  it  belongs  to  the  FIG.  55.  A  centipede, 

Branch  of  the  animal  kingdom  called  Scol°Pend™    SP-      (J;rom 

Specimen.)    From  Kellogg, 
arthropods 

Class,  insecta 
Order,  orthoptera 
Family,  acrididae 
Genus,  melanoplus 
Species,  femur-rubrum. 


174 


BIOLOGY  FOR  BEGINNERS 


k********^^ 
Onycophora 


.Ancestral  arthropod 

FIG.  56.  A  scheme  to  show  how  the  arthropods  have  developed  from  their 
ancient  ancestor.  The  branches  are  not  intended  to  represent  actual  relation- 
ships but  to  indicate  the  lines  of  specialization  which  have  been  followed. 
From  Pearse. 


We  do  not  have  to  learn  these  apparently  difficult  names.  What 
we  ought  to  try  to  understand  is  the  method  of  classification,  be- 
cause it  is  used  in  all  animal  and  plant  groups  and  is  so  well  il- 


ARTHROPODS  175 

lustrated  by  the  arthropods.  In  the  case  of  the  grasshopper,  the 
species  group  includes  just  that  one  kind  of  grasshopper  and  no 
others  so  they  are  alike  in  all  points;  the  genus  includes  several 
species  with  a  good  many  points  of  resemblance.  The  family  in- 
cludes the  members  of  several  genera  which  resemble  each  other 
but  less  closely  than  the  members  of  the  genus.  The  order,  or- 
thoptera,  includes  several  families  with  members  as  different  as 
the  cockroach,  locust,  katydid,  grasshopper,  and  crickets,  while 
the  class  insecta  includes  all  the  different  orders  of  insects,  such  as 
bees,  moths,  flies,  and  beetles  which  of  course  include  many  in- 
dividuals but  resemble  each  other  in  still  fewer  points.  As  stated 
before,  the  Insecta  is  one  of  the  three  classes  into  which  the  ar- 
thropod branch  is  divided  and  have  the  characteristics  of  that 
enormous  group,  in  common  with  the  acerata  and  Crustacea. 

Value  of  Scientific  Classification.  This  may  seem  very  com- 
plicated but  is  really  very  necessary,  for  if  there  were  no  way  of 
grouping  the  different  forms,  they  could  never  be  studied  or  un- 
derstood, much  less  named  and  identified.  Not  only  this,  but 
resemblance  in  points  of  structure  shows  actual  family  relationship, 
those  forms  most  alike  being  nearest  related  and  those  with  less 
points  in  common,  more  distantly  connected.  Classification  is  not 
only  a  convenient  arrangement  to  save  labor  in  the  study  of  living 
things,  but  shows  their  relationship  and  descent,  as  well. 

Let  us  classify  the  grasshopper  fully  according  to  this  outline, 
and  see  how  much  is  included  in  merely  its  proper  scientific 
classification. 

Kingdom:  Animal ' 
Branch:  Arthropoda  (jointed-foot  animals) 

Class:  Insecta  (body  "  cut  into  "  three  regions) 
Order:  Orthoptera  (straight-winged) 
Family:  Acrididae  (locust  family) 
Genus:  Melanoplus  (black  armored) 
Species:  femur-rubrum  (red-legged) 

From  just  the  translation  of  the  names  used,  one  can  obtain  a 
fair  description  of  the  animal  concerned,  and  if  the  characteristics 


176  BIOLOGY  FOR  BEGINNERS 

of  each  successive  group  are  known,  a  complete  description  is 
obtained. 

If  a  person  in  Africa  were  addressing  a  letter  to  this  country,  and 
gave  a  full  and  exact  address,  it  would  cover  as  many  items,  as  the 
following  comparison-  shows. 


Grasshopper 


Letter 


Kingdom:  Animal 
Branch:  Arthropoda 
Class:  Insecta 
Order:  Orthoptera 
Family    Acrididae 
Genus:  Melanoplus 
Species:  Femur-rubrum 


Nation :  United  States  of  America 

State:  Illinois 

City:  Chicago 

Street:  Madison 

Number:  3561 

Surname:  Smith 

First  name:  John  J. 


In  the  case  of  the  letter  as  many  items  have  been  mentioned  as 
with  the  scientific  classification,  and  for  the  same  purpose,  namely, 
that  both  shall  be  absolutely  definite  and  apply  to  one  only.  If, 
in  addition,  we  could  so  address  our  letters  that  the  appearance 
and  relationship  of  the  addressee  were  included,  it  would  cor- 
respond to  the  very  remarkable  system  of  classification  used  in  all 
biologic  work. 

Scientific  Names.  When  speaking  of  a  plant  or  animal  the  genus 
and  species  names  are  usually  all  that  are  given,  assuming  that  the 
relationship  to  the  larger  groups  will  be  known.  The  genus  is 
placed  first  and  begins  with  a  capital  letter,  the  species  follows, 
and  begins  with  a  small  letter  unless  it  be  from  a  proper  name. 
The  genus  name  is  usually  a  noun  and  the  species  name  an  adjec- 
tive; the  genus  name  precedes  the  species  name,  as  is  the  regular 
Latin  order.  We  follow  it  in  our  lists  of  names  in  all  formal  records 
where  John  J.  Smith  would  appear  as  Smith,  John  J.  Thus, 
Melanoplus  femur-rubrum  is  the  scientific  name  of  the  common 
grasshopper.  It  is  a  long  name,  even  for  a  scientific  one,  and  was 
chosen  on  that  account,  but  how  much  more  convenient  and  ac- 
curate than  saying  "  the  black-armored  grasshopper  with  red  legs." 

Another  advantage  of  scientific  names  is  that  they  are  uniform 


ARTHROPODS  177 

throughout  the  world.  People  of  all  languages  use  the  same  name 
for  the  same  plant  or  animal  in  their  scientific  works,  and  as  a 
result  there  is  no  confusion,  nor  any  need  for  learning  a  new  set  of 
names.  Common  local  names  are  always  uncertain,  for  there  are 
often  several  names  for  the  same  plant  or  animal.  With  the  scien- 
tific names  there  is  but  one  possible,  and  therefore  there  can  be 
no  chance  for  mistake. 
Scientific  names  have  these  advantages: 

1.  They  are  absolutely  definite. 

2.  They  are  used  by  people  of  all  languages. 

3.  They  are  usually  descriptive. 

4.  They  are  easier  to  study  than  separate  descriptions. 

5.  They  show  relationship  and  descent. 

COLLATERAL   READING 

Applied  Biology,  Bigelow,  pp.  358-404;  General  Zoology,  Linville  and 
Kelly,  pp.  138-156;  Animal  Studies,  Jordan,  Kellogg  and  Heath,  pp. 
109-129;  Economic  Zoology,  Kellogg  and  Doane,  pp.  106-125;  Economic 
Crustacea,  U.  S.  Fish  Commission  Report,  1889-1893;  Life  and  her  Chil- 
dren, Buckley,  pp.  153-177;  Zoology  Text,  Colton,  pp.  54-77;  Elementary 
Zoology,  Kellogg,  pp.  144-156;  Zoology  Text,  Shipley  and  MacBride,  pp. 
118-135;  Elementary  Zoology,  Galloway,  pp.  232-265. 

SUMMARY 

Meaning  of  name:  .  Number  of  members. 
Characteristics : 

1.  Jointed  appendages. 

2.  External  skeleton. 

3.  Three-body  regions. 

Head,  food-getting  and  sense  organs. 

Thorax,  locomotion. 

Abdomen,  reproduction,  less  specialized. 

4.  Dorsal  heart  and  ventral  nervous  system. 
Animal  Kingdom  divided  into 

1.  Branches,  which  are  divided  into 

2.  Classes,  which  are  divided  into 

3.  Orders,     4.    Families,     5.    Genera,     6.    Species. 
Note: 

Larger  groups  have  fewer  points  in  common,  more  individuals. 
Smaller  groups  have  more  points  in  common,  fewer  individuals. 
Smaller  groups  have  all  characteristics  of  the  larger  groups  of  which 
they  are  a  part,  and  certain  peculiar  to  their  own. 


178 


BIOLOGY  FOR  BEGINNERS 


Classes 

Characteristics 

Examples 

Crustacea 

Head-thorax  united 

Lobster 

Acerata 

Carapace,  gills 
Five  pair  legs 
No  carapace,  no  gills 
Four  pair  legs 
Air  sacs  or  tracheae 

Crayfish 
Crab,  shrimp 
Spiders 
Horseshoe-crab 

Insecta 

Head  and  thorax  separate 
Three  pair  legs;  wings 
Breathe  by  tracheae 

Beetles 
Grasshoppers 
Butterflies 

Classification: 

1.  Based  on  likeness  of  structure  (homology). 

2.  Hence  shows  relationship  and  descent. 

3.  Assists  in  study  and  placing  of  new  forms. 

Scientific  Name: 

1.  Consists  of  genus  and  species  names. 

2.  Avoids  long  descriptions. 

3.  Is  universally  used. 

4.  Makes  meaning  absolutely  definite. 

5.  Shows  relationship  of  different  forms. 


CHAPTER  XXII 

CRUSTACEA,  A   CLASS   OF  ARTHROPODS 

Vocabulary 

Carapace,   the   external   protective   covering   of   the   thorax   in 

Crustacea. 

Mandibles,  jaw-like  organs. 
Maxillae,  little  jaws,  aid  in  holding  food. 

Maxillipeds,  jaw-feet,  aid  in  catching,  holding,  and  chewing  food. 
Literally,  actually,  truly. 

Our  study  of  the  worms  showed  us  a  group  of  animals  in  which 
tissues  and  organs  had  become  somewhat  specialized,  circulator}- 
organs  developed,  and  adaptations  formed  for  an  inactive  under- 
ground or  parasitic  kind  of  life.  In  the  Crustacea  we  deal  with 
animals  such  as  crayfish,  lobster,  and  crab,  which  are  adapted  for 
an  active,  aquatic  (water)  life,  in  which  division  of  labor  among 
their  various  organs  has  been  carried  to  a  higher  point. 

CRAYFISH 

External  Structure.  The  crayfish,  which  we  will  study  as  a  type, 
has  the  body  covered  with  a  dark-colored,  limey,  external  skeleton 
'(exo-skeleton)  divided  into  two  regions,  the  cephalo-thorax  (head 
thorax)  being  covered  by  the  united  carapace,  and  the  abdomen 
made  up  of  seven  separate  movable  segments.  This  is  the  first 
animal  we  have  studied  which  has  had  any  skeleton  at  all  and  it 
may  seem  strange  to  find  it  on  the  outside  of  the  body  while  ours 
is  inside.  However  the  same  functions  are  performed  in  both 
cases,  namely  to  protect  the  organs  and  act  as  levers  for  the  muscles. 

Protection  is  most  important  in  the  Crustacea  which  really  have 
a  suit  of  mail,  such  as  the  knights  used  to  wear.  Their  joints  are 

179 


180 


BIOLOGY   FOR  BEGINNERS 


made  to  bend  by  the  same  arrangements,  only  better  adapted  than 
man's,  and  they  cover  their  head  and  body  by  a  shield  (carapace) 
far  lighter  and  more  efficient  than  ever  warrior  carried.  Not 
only  is  their  exo-skeleton  strong,  light,  and  flexible,  but  it  is  colored 
so  as  to  escape  notice  from  enemies  (protective  coloration).  It 
is  also  provided  with  sharp  spines  and  projects  downward  at  the 
sides,  thereby  guarding  the  gills  and  soft  under  parts  of  the  body. 
In  addition  to  its  protective  function,  the  skeleton  forms  a  rigid 


.     FIG.  57.    The  crayfish  —  a  type  of  Crustacea. 


series  of  levers,  by  means  of  which  a  complicated  system  of  muscles 
provides  for  swift  motion  and  locomotion,  essential  for  escape, 
attack,  and  food-getting.  The  development  of  a  skeleton  has 
also  enabled  its  possessor  to  advance  in  many  ways. 

As  stated  before,  the  body  consists  of  segments  (20  in  all)  though 
only  the  abdominal  ones  are  movable,  those  of  the  cephalo- thorax 
being  fused  (united)  together  for  greater  strength  and  protection, 
while  the  numerous  appendages  provide  for  the  needed  freedom  of 
motion.  Each  of  these  twenty  segments  has  a  pair  of  appendages, 


ARTHROPODS 


181 


antennule 


opening  of  green  (/land 


maxillipeds 


thorax 


genital  aperture 


'anus 

uropod 

—telson 


FIG.  58.    Ventral  aspect  of  crayfish  (Cambarus  sp.)  with  the  appendages  of 
one  side  disarticulated.     From  Kellogg. 


182  BIOLOGY  FOR  BEGINNERS 

most  of  which  are  adapted  for  different  purposes  (being  developed 
from  the  ordinary  swimming  leg)  as  is  shown  in  the  tabulation. 
The  front  of  the  carapace  extends  forward  into  a  protective  beak, 
the  rostrum  (why  so  called?) ,  on  either  side  of  which  are  the  eyes, 
set  on  movable  stalks  and  each  composed  of  many  lenses. 

Head  Appendages.  Beginning  at  the  anterior  (head)  end,  we 
first  come  to  the  small  and  large  feelers  (antennae)  at  whose  base 
open  the  ear  sacs  and  excretory  organs  respectively.  Then  come 
the  true  jaws  (mandibles)  and  two  pairs  of  little  jaws  (maxillae) 
which  aid  in  chewing  the  food.  To  the  posterior  maxilla  is  attached 
the  "  gill  bailer,"  a  scoop-shaped  organ  for  paddling  water  over 
the  gills,  the  flow  being  toward  the  anterior.  So  far,  the  organs 
named  belong  to  the  head.  Notice  the  various  functions  performed. 
Also  observe  that  the  jaws  work  from  side  to  side  and  not  up  and 
down,  because  they  are  merely  leg-like  appendages  adapted  for 
chewing  and  so  continue  to  have  a  horizontal  motion  as  do  the  legs. 

Thoracic  Appendages.  The  first  appendages  of  the  thorax  are 
three  pairs  of  maxillipeds  (jaw  feet)  whose  function  is  holding  and 
chewing  food.  To  these  are  attached  gills  for  respiration.  Next 
come  the  large  claws,  evidently  for  defence  and  food  getting,  then 
two  pairs  of  legs  with  claws  at  the  tip  and  two  more  pairs  with- 
out claws.  These  four  pairs  of  legs  are  concerned  mainly  with 
walking,  and  to  them  and  to  the  large  claws  as  well,  gills  are  at- 
tached, which  extend  up  under  the  carapace  into  the  gill  chamber. 

Abdominal  Appendages.  The  appendages  of  the  abdomen  are 
called  swimmerets  and  are  similar  on  the  first  five  segments,  being 
adapted  for  paddling  forward  in  the  water.  They  are  also  used  by 
the  female  for  attachment  of  her  eggs.  The  sixth  swimmeret  is 
enormously  developed  into  a  wide  fin  or  flipper  while  the  ap- 
pendage of  the  seventh  segment  is  reduced  to  a  mere  spine  and  the 
segment  itself  is  flattened.  The'  sixth  and  seventh  segments  to- 
gether form  a  powerful  organ  for  backward  locomotion,  for  they  can 
be  whipped  forward  by  the  strong  muscles  of  the  abdomen  and  the 
animal  will  shoot  backward  at  high  speed. 

Adaptation.  While  we  do  not  have  to  memorize  all  these  append- 
ages, there  are  two  lessons  that  their  study  must  teach;  first  how 


ARTHROPODS 


183 


FIG.  59.    The  appendages  from  the  entire  right  side  of  the  body  of  a  lobster, 
arranged  serially  to  illustrate  serial  homology.     From  Calkins. 


184  BIOLOGY   FOR   BEGINNERS 

remarkably  division  of  labor  may  be  carried  out,  and  second  that 
we  have  here  the  modification  of  one  kind  of  organ  for  many  uses. 
The  tabulation  will  show  how  many  and  how  varied  are  the  func- 
tions performed.  It  will  also  be  seen  that  these  various  organs  are 
developed  from  a  simple  kind  of  appendage  (the  swimmeret).  By 
the  addition  and  modification  of  segments,  organs  have  been  de- 
veloped as  widely  different  as  the  large  claws  and  the  antennae. 

Homology.  When  we  find  organs  (either  in  the  same  or  different 
animals)  which  were  developed  from  the  same  part,  that  is,  whose 
origin  and  structure  are  similar,  we  call  them  homologous  organs. 
Thus  we  may  say  that  the  antennae  and  claws  of  the  crayfish  are 
homologous  to  the  swimmerets,  or  that  our  arm  is  homologous  to 
the  foreleg  of  a  horse,  even  though  the  functions  are  so  different. 
This  word  is  the  mate  to  analogous  which  meant  similar  in  function. 
We  might  say  that  the  gills  of  the  crayfish  and  the  lungs  of  man 
are  analogous,  because  they  both  perform  the  function  of  respira- 
tion but  we  cannot  say  they  are  homologous,  since  the  gills  are  de- 
veloped from  the  legs,  while  the  lungs  are  outgrowths  of  the  throat. 

Internal  Structure.  Internally,  also,  there  is  a  considerable  de- 
gree of  specialization.  The  digestive  system  and  its  glands  occupy 
a  large  part  of  the  cephalo-thorax,  there  being  three  sets  of  kvth 
in  the  stomach,  to  complete  the  chewing  of  the  food  which  was 
begun  by  the  jaws.  A  well-developed  circulatory  system  and  a 
complicated  heart  mark  an  advance  along  this  line.  The  e\mitory 
and  reproductive  organs  are  present  and  fairly  developed.  The 
nervous  system,  though  similar,  is  much  more  specialized  than  in 
the  worms.  The  senses  of  touch  and  smell,  located  in  the  antennae, 
are  probably  acute.  The  eyes  are  on  movable  stalks  and  are  com- 
pound, each  consisting  of  numerous  lenses,  but  the  sight  is  prob- 
ably not  keen.  The  ears  are  located  at  the  base  of  the  antennae 
but  neither  hearing  nor  taste  seem  to  be  especially  developed. 

While  these  sense  organs  do  not  seem  very  efficient,  yet  enor- 
mous advance  can  be  seen  when  they  are  compared  with  the  earth- 
worm with  no  organs  of  special  sense  at  all.  The  worm  probably 
feels  only  touch  and  vibration  sensations  through  the  body  wall, 
with  a  possibility  of  taste  and  heat  or  light  sensations  in  the  region 


ARTHROPODS 


FIG.  60.    Longitudinal  section  of  the  lobster  showing  the  arrangement  of  the 
internal  organs.     From  Calkins. 


186  BIOLOGY  FOR  BEGINNERS 

of  the  head.  Since  the  degree  in  which  an  animal  can  get  in  touch 
with  its  environment  marks  the  stage  of  its  advancement,  the 
Crustacea  far  excel  the  worms  in  development. 

Locomotion.  This  function  is  provided  for  by  the  swimmerets 
which  carry  the  body  slowly  forward,  by  the  tail  flipper  which  drives 
it  swiftly  backward,  and  by  the  four  pairs  of  walking  legs  which 
can  travel  in  either  direction  and  sideways  as  well.  All  are  operated 
by  powerful  muscles,  assisted  by  the  exo-skeleton.  You  can  see 
why  the  slang  expression  "  to  crayfish  "  means  to  back  out  of  any 
agreement. 

Protection.  The  Crustacea's  adaptations  for  protection  are  the 
exo-skeleton  with  its  color  and  spines,  the  powerful  jaws  and  claws 
for  attack,  speed  for  escape,  fairly  keen  senses,  and  a  nervous 
system  to  guide  its  actions. 

Respiration.     Respiration   in   protozoa   was   accomplished   by 

contact  of  the  cell  with  dissolved  oxygen  in  the  water;  in  the  worm 

by  contact  of  the  body  wall  with  oxygen  in  the  air;  osmosis  was 

the  method  in  both  cases.    In  the  Crustacea  we  have  organs  called 

gills,  specially  developed  for  carrying  on  the  exchange  of  oxygen 

and  carbon  dioxide.    These  gills  are  thin  walled,  to  allow  osmosis, 

feathery  to  expose  much  surface,  provided  with  many  blood  vessels 

to  receive  oxygen  and  to  liberate  carbon  dioxide,  and  also  are 

arranged  to  insure  a  constant  flow  of  fresh  water  over  them.    This 

last  is  brought  about  in  part  by  the  gill  bailer,  attached  to  the 

second  maxilla  and  partly  by  the  gills  being  attached  to  the 

appendages.    These  move  in  the  water,  with  every  motion  of  a 

leg  or  maxilliped.    Finally,  as  the  water  passes  under  the  carapace 

from  behind  toward  the  head,  this  flow  is  aided  every  time  the 

animal  swims  backward.    The  gills  are  protected  by  the  carapace, 

which    extends    over    them   and   forms   a   chamber   which    will 

hold   moisture   for   some   time,   thus  keeping  them  alive  when 

removed  from  the  water.    Notice  the  importance  of  the  fact  that 

oxygen  is  soluble  in  water;    if  it  were  not,  the  aquatic  animals 

could  not  exist,  since  it  is  the  oxygen  dissolved  from  the  air, 

and  not  the  oxygen  of  the  water  (H^sO)  itself  which  all  water 

animals  use. 


ARTHROPODS  187 

Food-getting.  The  food  of  the  Crustacea  is  usually  animal, 
either  alive  or  dead,  some  even  being  cannibals,  while  others  act 
as  useful  scavengers.  A  few  of  the  smaller  forms  are  peaceful 
vegetarians.  Their  swiftness,  claws,  mouth  parts,  color  protection, 
and  sense  of  touch  and  smell  all  are  adaptations  for  food-getting 
and  their  large  number  shows  how  well  able  they  are  to  cope  with 
their  surroundings. 

Life  History.  The  eggs,  which  often  number  thousands,  are  laid 
by  the  female,  fertilized  by  sperms  from  the  male  as  they  are  laid, 
and  attached  to  the  swimmerets  where  they  are  carried  and  pro- 
tected by  the  mother  for  about  ten  months.  The  young  after  hatch- 
ing, which  occurs  in  summer,  cling  to  the  swimmerets  for  some  time. 
When  first  hatched  they  are  very  small,  not  entirely  like  the  adult 
in  structure,  and  they  remain  at  the  surface  of  the  water  for  the 
first  stages.  After  moulting  four  or  five  times,  they  settle  down  on 
the  bottom  among  the  rocks,  where  they  live  on  smaller  crus- 
taceans. During  these  early  stages  which  occupy  ten  to  fifteen 
days  they  are  nearly  defenceless  and  millions  are  destroyed  by 
other  aquatic  animals  for  food.  After  reaching  the  bottom  they 
are  somewhat  better  protected  though  still  destroyed  in  large 
numbers.  This  high  mortality  is  the  reason  for  the  production  of 
such  large  numbers  of  eggs.  During  their  life  at  the  bottom, 
moulting  occurs  at  longer  intervals  until  adult  size  is  reached  at 
the  age  of  five  years  (in  case  of  the  lobster)  after  which  they  do  not 
moult  oftener  than  once  in  one  or  two  years. 

Moulting.  This  moulting,  or  shedding  of  the  exo-skeleton  is  a 
direct  result  of  having  the  hard  parts  outside.  They  cannot  grow 
larger  except  by  shedding  their  armor,  and  this  is  a  point  in  which 
the  internal  skeleton  of  the  higher  animals  is  a  very  great  ad- 
vantage. With  it,  growth  may  be  continuous.  However,  the  exo- 
skeleton  provides  better  protection.  When  ready  to  moult,  the  lime 
is  partly  absorbed  from  the  skeleton;  the  carapace  splits  along  the 
back,  water  is  withdrawn  from  the  tissues  which  makes  them 
smaller  and  the  animal  literally  humps  itself  out  of  its  former 
skeleton,  leaving  behind  the  lining  of  its  stomach  and  its  teeth. 
Immediately  water  is  absorbed  and  growth  proceeds  very  rapidly. 


188  BIOLOGY  FOR  BEGINNERS 

The  lime  is  replaced  in  the  new  and  larger  armor  and  Richard  is 
himself  again.  Usually  the  later  moults  take  place  in  hidden 
locations  and  with  haste,  as  the  animal  is  totally  helpless  and  a 
prey  to  all  sorts  of  enemies  when  growing  its  new  suit.  It  is  at  this 
time  that  "  soft  shell  crabs  "  are  caught,  which  are  merely  the 
ordinary  crab  in  the  act  of  moulting. 

Reproduction  of  Lost  Parts.  In  moulting  or  in  battle  with 
enemies,  it  often  happens  that  appendages  are  lost  or  injured,  in 
which  case  the  limb  is  voluntarily  shed  between  its  second  and 
third  segments.  A  double  membrane  prevents  much  loss  of  blood, 
and  a  whole  new  appendage  is  developed  to  replace  the  injured 
member.  This  accounts  for  the  common  sight  of  crayfish,  etc., 
with  one  claw  much  smaller  tha"n  its  mate. 

This  reproduction  of  lost  parts  depends  upon  the  degree  of  com- 
plexity of  the  part.  The  earthworm  may  be  able  to  regrow  the 
whole  posterior  of  its  body  while  a  starfish  can  develop  all  its  or- 
gans if  one  ray  and  its  base  be  left.  The  hydra  and  corals  nor- 
mally reproduce  by  budding  off  new  individuals  and  the  protozoa, 
simplest  of  all,  regularly  reproduce  the  whole  animal  by  division 
in  two  parts.  On  the  other  hand,  higher  forms,  such  as  man,  have 
tissues  so  highly  specialized  that  we  cannot  even  grow  a  new 
finger.  The  best  we  can  do,  is  to  develop  scar  tissue  to  fill  a  wound, 
or  grow  new  hair,  nails,  skin,  and  (once  only)  teeth.  This  is  one 
penalty  for  high  specialization. 


COLLATERAL    READING 
(Crayfish  and  Lobster) 

N  Y.  State  Forest,  Fish  and  Game  Report  (1898),  p.  290;  U.  S.  Fish 
Commission  Report  (1898),  p.  229;  Invertebrate  Morphology,  McMur- 
rich,  p.  377;  Advanced  Text,  Claus  and  Sedgwick,  p.  461;  Invertebrate 
Anatomy,  Huxley,  pp.  265-293;  Advanced  Text,  Parker  and  Haswell 
(Vol.  I),  pp.  498-514;  Advanced  Text,  Packard,  pp.  226-272;  Animal 
Forms,  Jordan  and  Kellogg,  pp.  93-104;  Animal  Studies,  Jordan,  Kel- 
logg and  Heath,  pp.  109-120;  Animal  Activities,  French,  pp.  101-114; 
Elementary  Text  (Zoology},  Kellogg,  pp.  144-155;  Elementary  Text  (Zo- 
ology), Colton,  pp.  61-86;  Elementary  Text  (Zoology),  Linville  and  Kelly, 
pp.  125-156;  Elementary  Text  (Zoology),  Morse,  pp.  130-147;  Elementary 
Text  (Zoology),  Needham,  pp.  111-129;  Elementary  Text  (Zoology),  Daven- 


ARTHROPODS 


189 


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190  BIOLOGY  FOR  BEGINNERS 

port,  pp.  120-152;  Economic  Zoology,  Osborne,  pp.  174-200;  Economic 
Zoology,  Kellogg  and  Doane,  pp.  106-125;  Applied  Biology,  Bigelow,  pp. 
358-376;  Life  and  Her  Children,  Buckley,  Chap.  VIII;  Animal  Life, 
Thompson,  p.  25;  Seashore  Life,  Mayer,  pp.  77-112;  Life  in  Ponds 
and  Streams,  Furneaux,  pp.  179-200;  Talks  About  Animals,  pp.  3-45; 
The  Crayfish:  an  Introduction  to  Zoology,  Huxley,  entire;  Practical 
Zoology,  Davison,  Chap.  IX. 


SUMMARY 

Contrast,  worms,  having  only  simpler  tissues  and  organs,  no  skeleton, 

inactive. 

Crustacea,  with  high  specialization,  skeleton,  active,  aquatic. 
Characteristics: 

External  skeleton  adapted  for  protection. 
Jointed  appendages  adapted  for  rapid  motion. 
High  specialization  adapted  for  division  of  labor. 
Gills  and  connected  organs  adapted  for  aquatic  life. 
Crayfish  (as  type  of  Crustacea). 
External  Structure: 

Exo-skeleton,  for  protection  and  to  act  as  levers  for  muscles. 
Protective  adaptations: 
Hard,  limy,  color,  spines, 
Projection  over  gills  and  abdomen. 
Carapace,  rostrum. 
Lever  adaptations: 
Hollow,  strong,  light, 
Hinge  joints  in  all  directions. 
Body  regions,  cephalo- thorax  and  abdomen. 
Cephalo-thorax : 

Includes  head  and  thorax,  13  segments, 
United  for  strength,  rostrum  for  protection. 
Carapace  over  anterior  and  gills. 
Head  appendages: 
Sense  organs. 

Antennules,  antennae,  for  feeling  or  smell. 
Eyes,  ear  sacs,  sense  hairs. 
Mouth  parts. 

Mandibles,  one  pair  for  chewing. 
Maxillae,  two  pair  aid  in  holding  food. 
Maxillipeds,  three  pair,  catching  and  chewing  food. 
Thoracic  appendages. 

Maxillipeds,  three  pair,  holding  and  chewing  food. 
Large  claws,  defence  and  food  getting. 
Clawed  feet,  two  pair,  locomotion,  prehension. 
Unclawed  feet,  two  pair,  locomotion. 
(Gills  on  all  above  appendages.) 


ARTHROPODS  191 

Abdominal  appendages: 

Swimmerets,  five  pair  for  swimming  and  egg  attachment. 
Tail  fin,  sixth  and  seventh  pairs,  backward  motion. 
Study  of  appendages  shows 

1.  Modification  of  similar  part,  swimmeret,  for  different  uses 

(Homology). 

2.  Adaptation  for  different  functions  (specialization). 

3.  Division  of  labor  among  homologous  parts. 
Homology,  likeness  in  structure  and  origin,  shows  relationship. 
Analogy,  likeness  in  function,  not  necessarily  in  structure. 

Adaptations  of  Crayfish  for 

1.  Locomotion. 

Swimming  forward  by  means  of  swimmerets. 
Swimming  backward  by  means  of  tail  fin. 
Walking  either  forward,  backward,  or  sidewise. 

2.  Protection. 

External  skeleton,  color,  spines,  carapace,  projecting  sides, 
speed,  claws. 

3.  Food-getting  (what  food?) 

Claws,  speed,  mouth-parts,  senses,  color. 

4.  Respiration  (cf.  protozoa  and  worms). 

Gills,  adapted  by  being  thin;   for  osmosis 
Being  well  supplied  with  blood. 
Being  protected;  large  surface. 
Water  current  provided  by 
Gill  bailer. 

Locomotion  backward. 
Leg  motion  in  all  directions. 

5.  Sensation. 

Eyes,  ears,  feelers,  hairs. 
Life  History: 

1.  Egg  fertilized,  attached  to  swimmeret  (protection,  aeration). 

2.  Hatch  in  summer,  remain  attached  to  mother. 
3     Grow  by  moulting  (reason). 

4.  Top  swimmers  when  young,  then  on  bottom. 

5.  Why  so  many  eggs  needed. 
Moulting: 

Reason  (cf.  internal  skeleton). 
Process:  Absorption  of  lime  from  shell. 

Carapace  splits. 

Water  withdrawn  from  tissues,  causing  shrinkage. 

Humps  out  of  shell. 

Re-absorption  of  water  and  rapid  growth. 

Hasty  formation  of  new  skeleton. 
Lost  Parts  Reproduced: 

What  animals  can  reproduce  lost  parts? 

Why  not  so  much  in  higher  forms?     (Greater  specialization.) 

What  tissues  can  man  reproduce? 


CHAPTER  XXm 

OTSECTA,  A   CLASS   OF  ARTHROPODS 

Vocabulary 

Trachea,  a  breathing  tube,  admitting  air  to  the  tissues.  Plural: 
tracheae. 

Chitin,  a  horn-like,  elastic  substance  found  in  the  external  skeletons 
of  insects  and  other  arthropods,  pronounced  "kite-in." 

Accessory,  additional  or  assistant  organs. 

Palpus,  feeler  or  sense  organ  attached  to  the  mouth  parts  of  in- 
sects, etc.  Plural:  palpi. 

Spiracles,  external  openings  of  the  tracheae,  used  in  breathing. 

Ganglion,  a  mass  of  nerve  tissue.     Plural:  ganglia. 

The  Insects  include  that  division  of  the  Arthropods  which  have 
head,  thorax,  and  abdomen  separate,  one  pair  of  antennae,  three 
pairs  of  legs,  usually  two  pairs  of  wings,  and  which  breathe  by 
means  of  tubes  called  tracheae.  This  group  includes  more  species 
than  all  the  other  living  animals  together,  there  being  about  300,000 
kinds  known  already.  Experts  regard  this  as  not  more  than  one- 
fifth  of  all  in  existence.  Not  only  are  there  many  kinds  of  insects, 
but  each  kind  produces  myriads  of  individuals  like  the  locusts  and 
mayflies,  whose  swarms  darken  the  sky.  Their  struggle  for  ex- 
istence is  very  severe  and  this  results  in  manifold  adaptations  of 
structure. 

High  Specialization.  Highly  specialized  mouth  parts  for  dif- 
ferent kinds  of  food,  wonderful  leg  and  wing  development  for 
swift  locomotion,  marvelous  instincts  and  complicated  internal 
structure  are  some  of  the  lines  along  which  insects  have  developed 
in  order  to  survive  among  their  countless  competitors  in  the  race 
of  life.  Some  are  adapted  for  aquatic  life,  some  take  refuge  by 
burrowing,  some  live  in  colonies  like  bees  and  ants,  others  fight 
their  battles  alone;  some  have  become  swift  in  running,  leaping, 
or  flight,  while,  others  have  fallen  back  on  parasitic  laziness. 


INSECTA,   A   CLASS  OF  ARTHROPODS 


193 


Classification.  We  cannot  study  all,  or  even  one,  species 
thoroughly.  However  the  accompanying  table  will  show  the 
names  and  representatives  of  a  few  of  the  sixteen  different  orders, 
and  then  we  shall  take  up  two  or  three  types  in  greater  detail. 


Order 

Orthoptera 
Pseudo-neuroptera 
Hemiptera 
Diptera 
Coleoptera 
Lepidoptera 
Hymenoptera 

antennae 
/'  \ 


Representative 

grasshopper  —  cricket  —  locust 
dragon-flies 

true  bugs  —  lice  —  scale  insects 
flies  —  mosquitoes  —  fleas,  gnats 
beetles 

moths  —  butterflies 
bees  —  ants  —  wasps 


auditory  organ 
ocellus  : 

•'  head    compound  eye  I 


—ovipositor 


femur* 
tibia-'' 

torsal  segments 

FIG.  61.    Locust  (enlarged)  with  external  parts  named.    From  Kellogg. 

The  Grasshopper.  The  grasshopper  (which  really  is  a  locust) 
will  be  taken  as  a  type  of  all  the  insects.  It  belongs  to  the  order 
Orthoptera,  which  means  "  straight  winged  "  and  refers  to  the 
narrow  folded  wings,  held  straight  along  the  body. 

Exoskeleton.  As  in  all  Arthropods,  the  skeleton  is  external, 
but  differs  from  the  crayfish  in  that  it  contains  no  lime.  It  consists 


194 


BIOLOGY  FOR  BEGINNERS 


entirely  of  a  light,  tough  and  horny  substance  called  chitin  which 
is  usually  protectively  colored.  The  head,  with  its  sense  organs 
and  mouth  parts,  the  thorax  with  its  legs  and  wings,  and  the  ab- 
domen, with  its  vent  and  reproductive  organs,  are  all  readily 
distinguished. 

Head 

Sense  Organs.  The  antennae  are-  the  most  anterior  append- 
ages and,  as  usual,  are  many  jointed  and  devoted  to  the  senses 
of  touch  and  smell.  There  are  two  kinds  of  eyes,  three  simple 

ones  located  respectively  at  the  base 
of  each  antenna  and  on  the  ridge  be- 
tween them,  and  the  large  compound 
eyes  projecting  from  the  sides  of  the 
head  and  consisting  of  hundreds  of 
six-sided  lenses.  The  shape,  location, 
and  number  of  lenses  in  the  eye  seem 
to  adapt  the  insect  for  sight  in  several 
directions  at  once,  but  the  image 
formed  cannot  be  very  sharp. 

Mouth  Parts.  The  mouth  parts  of 
the  grasshopper  are  fitted  for  biting 
and  chewing  hard  foods  and  consist 
of  labrum,  mandibles,  maxillae,  and 
labium,  named  in  order  from  the 
anterior.  Though  the  mouth  parts  of  insects  are  very  greatly 
modified  to  suit  all  kinds  of  food,  still  these  four  sets  of  organs  are 
always  present,  so  we  must  become  familiar  with  their  names  and 
appearance. 

The  labrum  is  the  two-lobed  upper  lip  which  fits  over  the  strong, 
toothed,  horizontal  jaws  or  mandibles.  The  pair  of  maxillae,  or 
accessory  jaws,  are  next  behind  the  mandibles.  They  aid  in  cutting 
and  holding  food,  and  also  have  a  sense  organ,  like  a  short  antenna. 
This  is  called  a  palpus  (plural:  palpi).  Posterior  to  the  maxillae 
comes  the  labium  or  lower  lip,  a  deeply  two-lobed  organ,  also 
provided  with  palpi,  which  aids  in  holding  food  between  the  jaws. 


FIG.  62.  Part  of  coraeal 
cuticle,  showing  facets,  of  the 
.compound  eye  of  a  horsefly, 
Therioplectes  sp.  (Photomicro- 
graph by  Mitchell;  greatly 
magnified.)  From  Kellogg. 


INSECTA,   A   CLASS  OF   ARTHROPODS 
G7MSS  HOPPED 


195 


LP 


L.    1-AB.Run. 
M«t.    MANDIBLES. 

MX       M  AX  I  Ll_  AE  . 

M.P.    MAXILLARY    -PALPI 
L.P.     LABIAL    PAL.PI 

Lab.     LABlUfl. 


Lob. 


FIG.  63.     Grasshopper. 

Part  I.    Mouth  Parts. 

The  upper  lip  or  labrum  is  a  thin  scoop-shaped  organ,  which  helps  to  hold 
food  between  the  jaws. 

The  mandibles  or  jaws,  are  very  thick  at  the  edge,  sharply  toothed  and 
operated  by  powerful  muscles.  They  are  dark  brown  in  color  and  hard  enough 
to  gnaw  dry  wood. 

The  maxillae  or  accessory  jaws  are  very  complicated  organs  consisting  of 
two  sharp  hook-shaped  parts  backed  by  a  sort  of  hood.  These  help  in  hold- 
ing food  and  perhaps  in  chewing  it,  too.  Back  of  the  hood  are  the  palpi,  whose 


196  BIOLOGY   FOR  BEGINNERS 

tips  bear  sense  hairs,  and  perhaps  enable  the  grasshopper  to  judge  of  the  kind 
of  food  he  may  be  eating. 

The  "tongue"  or  hypopharynx  in  the  center,  fits  closely  in  the  throat  and 
seems  to  act  as  a  sort  of  piston  in  helping  to  suck  in  the  food  particles. 

The  labium  or  lower  lip,  like  the  upper  one,  helps  hold  the  food  in  place, 
but  is  much  larger  and  has  a  pair  of  palpi,  like  those  on  the  maxillae. 

Such  mouth  parts  are  typically  for  biting  and  chewing  and  are  similar  to 
those  found  in  many  beetles,  also. 

Part  II.    The  Leaping  Leg. 

The  two  short  segments  next  the  body  are  called  the  coxa  and  trochanter. 
Their  function  is  to  give  freedom  of  motion  to  the  base  of  the  leg  and  to  set  it 
out  a  little  from  the  side  of  the  body  so  that  it  can  push  directly  backward  in 
jumping. 

The  thick  part  is  the  femur  and  contains  some  very  powerful  muscles,  though 
the  body  muscles  also  help  in  jumping. 

The  tibia  is  the  long  thin  part  and  is  provided  with  backward  projecting 
spines  which  prevent  back  sliding  and  aid  in  cliirbing  through  grass. 

The  foot  consists  of  several  tarsal  joints  with  flexible  pads  and  backward 
projecting  spines  which  prevent  slipping  just  like  the  spiked  shoes  of  the  human 
jumper.  The  claws  at  the  end  aid  in  this  and  also  in  climbing. 

The  knee  and  ankle  joints  move  only  in  one  plane,  but  the  joints  next  the 
body  can  move  sidewise  also. 

Thorax 

The  thorax  consists  of  three  segments,  the  pro-,  meso-  and  meta- 
thorax.  The  prothorax  is  a  large  saddle-shaped  segment  to  which 
the  head  is  attached  and  bears  the  first  pair  of  legs;  the  middle 
or  mesothorax  bears  a  pair  of  legs  and  the  first  pair  of  wings;  while 
the  last  segment  (metathorax)  bears  the  leaping  legs  and  the  last 
pair  of  wings. 

Legs.  Each  of  these  six  legs  consists  of  five  parts  or  segments, 
connected  by  strong  joints  and  adapted  for  locomotion  by  walking, 
while  the  posterior  pair  is  also  enormously  developed  for  leaping. 
The  feet  (tarsi)  are  provided  with  spines,  hooks,  and  pads  to  give 
firm  grip  when  jumping  or  crawling.  A  joint  near  the  body  almost 
like  a  "  ball  and  socket "  permits  sufficient  freedom  of  motion. 

Wings.  The  anterior  (mesothoracic)  wings  are  long,  narrow, 
and  rather  stiff.  They  protect  the  more  delicate  under  wings  and 
act  as  planes  in  aiding  flight  and  leaping.  The  posterior  (meta- 
thoracic)  wings  are  thin  and  membranous.  They  are  supported 


INSECTA,   A   CLASS  OF  ARTHROPODS  197 

by  many  veins  and,  when  not  in  use,  are  folded  lengthwise,  like  a 
fan,  beneath  the  narrower  anterior  wings. 


Abdomen 

The  abdomen  consists  of  ten  movable  segments,  each  composed 
of  an  upper  and  lower  part,  united  by  a  membrane  which  allows 
it  to  expand  and  contract  in  the  process  of  breathing.  There 
are  no  jointed  appendages  as  on  the  head  and  thorax,  but  eight 
of  the  segments  have  breathing  pores  (spiracles)  on  each  side. 
The  segment  next  to  the  thorax  bears  the  ears  which  are  large 
membrane-covered  cavities  on  either  side. 

The  extreme  posterior  segments  in  the  female  bear  two  pairs  of 
hard  and  sharp-pointed  organs  called  ovipositors  (egg  placers) 
whose  function  is  to  dig  a  hole  in  the  ground  in  which  the  eggs  are 
laid.  The  males  have  no  such  organs  but  the  posterior  of  the  ab- 
domen is  enlarged  and  rounded  upward. 

Active  Life.  The  activity  of  insects  is  well  known  but  little  ap- 
preciated. They  have  the  most  enduring  and  powerful  muscles 
of  any  animal,  in  proportion  to  their  size.  Think  of  the  long  swift 
flight  of  bees,  often  extending  for  miles,  at  enormous  speed;  think 
of  the  loads  carried  by  ants  and  beetles;  of  the  hard  labor  done  by 
boring  and  burrowing  insects,  —  then  compare  their  size  and 
weight  with  our  own  and  see  how  fast  we  ought  to  fly  or  run,  how 
far  we  should  jump,  or  how  much  we  should  carry,  if  we  had  their 
muscular  ability.  Of  course  their  enormous  activity  requires  a 
great  deal  of  energy  which  means  that  they  must  use  a  large  amount 
of  food,  and  this,  in  turn,  implies  a  complete  digestive  apparatus. 
The  digested  food  requires  oxygen  to  oxidize  it  and  liberate  its 
energy  and  this  requires  a  perfect  system  for  breathing  to  supply 
the  oxygen.  To  control  such  a  powerful  high-speed  engine,  a  well- 
developed  nervous  system  is  also  demanded. 

The  foregoing  sounds  like  the  "  House  that  Jack  Built "  but  is 
an  outline  of  just  what  we  find  to  be  the  case,  not  only  in  insects 
but  in  all  higher  forms.  It  is  merely  another  instance  of  our  order 
of  study,  "  Structure,  Function,  Adaptation." 


198  BIOLOGY  FOR  BEGINNERS 

Internal  Structure.  The  internal  structure  is  very  complex,  some 
insects  having  over  twice  as  many  separate  muscles  as  we  have  in 
our  whole  body.  The  digestive  system  is  well  developed,  there 
being  salivary  glands,  a  crop,  stomach,  digestive  glands,  intestine, 
ancf  rectum. 

Excretion  is  provided  for  by  a  large  number  of  thread-like  tubes 
at  the  junction  of  stomach  and  intestine.  Circulation,  while  not 
entirely  inclosed  in  blood  vessels,  is  controlled  by  a  six-chambered 
heart  on  the  dorsal  (upper)  side,  from  which  the  light-colored  blood 
is  forced  toward  the  head  and  around  throughout  the  tissues,  in 
contact  with  the  air  tubes. 

Respiration.  The  respiratory  system  is  highly  developed.  It 
consists  of  an  extensive  network  of  air  tubes  called  tracheae,  there 
being  six  main  tubes  running  lengthwise,  from  which  branch  air 
sacs  and  smaller  tracheae  reach  every  tissue  in  the  body. 

These  tracheae  open  by  means  of  the  spiracles,  which  are  tiny 
holes,  protected  from  dust  by  hairs,  found  on  the  abdomen  (8  pairs) 
and  on  the  thorax  (2  pairs).  By  alternate  expansion  and  contrac- 
tion of  the  segments  at  the  rate  of  sixty-five  per  minute  air  is 
pumped  in  and  out  of  these  spiracles,  and  circulates  through  the 
tracheae,  where,  by  osmosis,  the  oxygen  from  the  air  and  carbon 
dioxide  from  the  blood  exchange  places.  A  peculiar  feature  of  the 
insect  respiration  is  the  fact  that  the  air  goes  to  the  blood  by  means 
of  the  tracheae  instead  of  the  blood  going  to  the  air  in  capillaries 
as  in  our  lungs.  Another  curious  fact  is  that  the  veins  of  the  wings 
are  probably  tracheae,  adapted  for  the  function  of  support  rather 
than  respiration. 

Nervous  System.  The  nervous  system  of  insects  reaches  a 
higher  degree  of  development  than  that  of  any  invertebrate  group 
and  a  comparison  of  the  types  studied  can  well  be  made  at  this  time. 

The  protozoan  cell  received  its  impressions  directly,  it  responded 
throughout,  to  heat,  light,  contact,  and  possibly  other  stimuli, 
but  vaguely  and  without  the  aid  of  any  nervous  tissue. 

In  animals  like  the  hydra,  certain  groups  of  cells  seem  more 
sensitive  than  others  to  external  influences  and  also  appear  to 
control  the  activities  of  the  animal.  These  are  the  simplest  ex- 


INSECTA,   A  CLASS   OF   ARTHROPODS  199 

amples  of  a  nervous  system  and  might  be  regarded  as  uncon- 
nected nerve  ganglia. 

In  the  worms  each  segment  has  its  nerve  mass  or  ganglion,  but 
all  are  connected  by  a  double  nerve  fiber  and  each  sends  out  many 
branches  to  various  organs,  which  are  thus  controlled.  Then, 
too,  in  the  worms,  there  is  a  larger  ganglion  in  the  anterior  end, 
above  the  mouth,  which  sends  special  nerves  to  the  mouth  parts 
and  skin.  Although  there  are  no  special  organs  of  sensation,  and 
the  structure  is  very  primitive,  there  is,  nevertheless,  an  organ 
corresponding  to  a  brain. 

In  the  Crustacea,  the  head  ganglion,  or  brain,  is  located  at  the 
base  of  the  rostrum.  It  is  much  larger  than  in  worms  and  has 
branches  extending  to  the  eyes,  ears,  antennae,  and  mouth  parts. 
This  brain  is  connected  with  ganglia  along  the  under  side  of  the 
body  but  instead  of  having  one  for  each  segment,  as  in  the  worms, 
they  are  combined  into  eleven  larger  and  more  complicated  nerve 
masses. 

In  the  insects  this  combination  of  ganglia  has  gone  farther  still. 
Including  the  brain  there  are  two  ganglia  in  the  head,  three  in  the 
thorax,  and  five  in  the  abdomen,  and  the  brain  and  sense  organs 
are  much  more  specialized  in  function. 

If  we  could  study  more  kinds  of  animals  we  would  observe  this 
general  tendency  toward  increasing  the  development  of  the  head 
ganglia,  of  combining  others  and  reducing  their  number,  while 
increasing  their  ability,  and  the  development  of  more  efficient 
sense  organs  and  greater  motion  control. 

As  soon  as  the  simplest  animal  forms  developed  far  enough  to 
have  one  end  always  go  forward  (anterior)  in  locomotion,  then 
that  end,  naturally,  "'ran  into"  contact  with  its  environment. 
So,  at  the  anterior  end  the  sense  organs  could  be  most  useful,  which 
is  the  reason  for  this  headward  tendency  in  development. 

In  all  animals  the  nervous  system  performs  two  general  func- 
tions; it  receives  and  appreciates  impressions  from  without  (sen- 
sation), and  causes  and  controls  motions  from  within  (motor  im- 
pulses) .  As  the  animals  increase  in  complexity,  the  nervous  system 
correspondingly  develops.  As  the  complexity  increased,  there  was 


200 


BIOLOGY  FOR  BEGINNERS 


greater  need  of  one  controlling  region,  so  that  all  the  body's  nu- 
merous functions  could  operate  in  harmony  and  as  a  result  the 
need  of  a  brain  developed.  Its  location,  as  explained  above,  was 
almost  of  necessity  in  the  "  head  "  or  anterior  end  of  the  animal. 


FIG.  64.  Developing  stages,  after  hatching,  of  a  locust,  Mdanoplus  femur- 
rubrum,  a,  just  hatched,  without  wing-pads;  6,  after  first  moulting;  c,  after 
second  moulting,  showing  beginning  wing-pads;  d,  after  third  moulting;  e, 
after  fourth  moulting;  /,  adult  with  fully  developed  wings.  (After  Emerton; 
younger  stages  enlarged;  adult  stage,  natural  size.  From  Kellogg.) 

Life  History.  The  eggs  are  fertilized  internally,  and  are  deposited 
in  two  masses,  protected  by  a  gum-like  substance,  in  holes  which 
the  female  digs  in  the  earth  with  her  ovipositor.  From  twenty  to 
thirty  eggs  are  thus  deposited  in  the  fall,  and  hatch  the  following 
spring.  This  illustrates  a  twofold  advantage  of  egg  reproduction, 
for,  not  only  is  the  number  of  individuals  increased,  but  they  pass 


INSECTA,  A  CLASS  OF  ARTHROPODS  201 

the  winter  safely  in  the  protected  egg,  while  most  of  the  adults 
are  frozen  to  death.  The  young  (nymph),  though  small,  red, 
and  wingless,  still  resembles  the  adult  in  most  respects,  but  as 
is  often  the  case  with  the  young,  the  head  is  disproportionately 
large.  As  with  all  arthropods,  they  grow  by  moulting,  usually 
five  times,  and  at  each  step,  develop  in  size  and  wings  till  they 
reach  full  growth.  The  moulting,  which  takes  about  half  an  hour, 
is  followed  by  rapid  growth  and  formation  of  a  new  exo-skeleton, 
the  former  one  having  split  along  the  thorax  to  allow  the  exit  of 
the  growing  insect.  It  emerges  head  first  but  very  weak  and  limp, 
and  often  does  not  survive  the  process. 

Metamorphosis.  In  many  animals  the  development  from  egg 
to  adult  passes  through  more  or  less  distinct  stages  instead  of 
being  a  gradual  increase  in  size.  Such  a  life  history  is  called  a 
metamorphosis. 

Among  insects  these  stages  may  be  several  in  number  and  the 
differences  between  them  slight,  as  in  the  grasshopper,  or  there  may 
be  four  definite  and  distinct  stages,  the  egg,  larva,  pupa,  and  adult 
as  found  in  the  butterfly,  for  example.  The  former  type  is  called 
an  incomplete  metamorphosis,  the  latter  a  complete  metamorphosis. 

Economic  Importance.  The  members  of  the  order  to  which 
the  grasshopper  belongs  (orthoptera)  are  with  one  exception,  all 
harmful  to  man.  Their  food  is  mostly  cereal  grains  or  crop 
plants,  which  they  often  destroy  over  wide  areas.  Locusts  and 
grasshoppers  have  been  a  plague  since  ancient  times.  They  are 
often  referred  to  in  Scripture  and  the  second  chapter  of  Joel  con- 
tains a  very  vivid  description  of  the  destruction  wrought  by  a 
swarm  of  locusts.  The  only  useful  relative  is  the  mantis,  which 
is  carnivorous  and  eats  other  insects,  many  of  which  are  harmful. 

COLLATERAL   READING 

Life  History  of  American  Insects,  Weed,  pp.  67-81 ;  Insect  Book,  Howard, 
pp.  334-340;  Insect  Life,  Comstock,  pp.  70-233;  Manual  of  Insects, 
Comstock,  pp.  104-118;  Guide  to  Study  of  Insects,  Packard,  pp.  556-572; 
Lessons' in  Zoology,  Needham,  p.  48;  Textbook  of  Zoology,  Parker  and 
Haswell,  Vol.  I,  p.  584;  Textbook  of  Zoology,  Packard,  p.  308;  Animal 
Forms,  Jordan  and  Kellogg,  p.  117;  Animal  Life,  Jordan  and  Kellogg, 


202  BIOLOGY  FOR  BEGINNERS 

p.  234;  Textbook  of  Zoology,  Linville  and  Kelly,  pp.  11-14;  Elemen- 
tary Zoology,  Kellogg,  pp.  161-163;  Injurious  Insects,  Treat,  p.  269; 
Injurious  Insects,  Saunders,  p.  157;  Introduction  to  Zoology,  Daven- 
port, pp.  1-4;  Economic  Zoology,  Smith,  pp.  11-51,  79-100;  Economic 
Zoology,  Kellogg  and  Doane,  pp.  14-25;  Descriptive  Zoology,  Colton,  Chap. 
I-III;  Practical  Zoology,  Davison,  Chap.  I-VII;  Farm  Bulletins,  Nos. 
47,  59,  70,  80,  132,  209,  211,  247,  264,  284. 


SUMMARY 
Characteristics  of  Insects: 

Separate  head,  thorax,  and  abdomen. 
One  pair  antennae,  three  pair  legs. 
Usually  two  pair  wings. 
Breathe  by  means  of  tracheae. 

High  degree  of  specialization  (adaptation)  because  of 
Severe  struggle  for  existence,  because  of 

Very  large  number  of  species  and  individuals. 

Specialized  for  various  foods: 

Vegetable  foods  Grasshopper  (biting) 

Blood  suckers  Mosquitoes 

Sap  suckers  Bugs  and  scale  insects 

Scavengers  Flies  and  beetles 

Nectar  Bees  and  moths 

Specialized  for  locomotion: 

Crawling  Beetles,  etc. 

Flying  Bees,  etc. 

Jumping  Grasshopper 

Swimming  Beetles  and  some  bugs 

Water  surface  Striders 

Burrowing  Ants,  etc. 

Specialized  instincts: 

(See  references  on  Bees,  Ants,  Wasps,  Termites). 
General  Structure: 

1.  Exo-skeleton,  chitin,  light,  strong,  and  protective  colored. 

2.  Regions: 

Head  for  sense  and  food-getting  organs. 
Thorax  for  locomotion  (respiration). 
Abdomen  for  reproduction  and  breathing  (ear). 
Head: 

Antennae,  one  pair,  functions,  cf.  crayfish. 
Eyes,  simple,  three,  location, 
compound,  structure,  why  not  on  stalks? 


INSECTA,  A  CLASS  OF  ARTHROPODS  203 

Mouth-parts  (biting). 

Upper  lip,  Labrum,  for  holding  food. 

True  jaws,  Mandibles,  for  chewing. 

Accessory  jaws,  Maxillae,  to  aid  jaws  (palpi). 

Lower  lip,  Labium,  to  hold  food  (palpi). 

Thorax. 

Anterior  thorax,          Prothorax,  Movable;  legs  attached. 

Middle  thorax,  Mesothorax,          Strong;  wings  and  legs. 

Posterior  thorax,        Metathorax,          United  to  mesothorax  wings  and 

jumping  legs. 
Legs, 

Functions:    walking,  clinging,  leaping. 

Structure. 

Adaptations: 

Strength  of  muscles. 
Length  of  leverage. 
Free  backward  movement. 
Spines,  pads,  etc. 
Point  of  attachment. 

Wings. 

First  pair,  planes  and  protection,  concave,  stiff,  straight. 
Second  pair,  thin,  folded  fan- wise,  propellers. 

Abdomen  (structure). 

Adaptations  for  respiration,  spiracles,  motion  of  segments. 
Adaptations  for  reproduction,  ovipositors. 
Adaptations  for  hearing,  ears. 

Activity  requires  energy. 

Energy  requires  food  to  supply  it. 

Food  requires  oxygen  to  release  its  energy. 

Oxygen"  supply  requires  good  breathing  organs. 
All  this  energy  requires  high  nerve  control. 

Internal  Structure. 

Muscles,  complex,  strong,  and  very  numerous. 
Digestion,  glands,  crop,  stomach,  caeca,  intestine,  rectum. 
Excretion,  malpighian  tubes. 

Circulation,  open  system,  dorsal,  light  color  blood. 
Respiration,  spiracles,  trachea,  motion  of  abdomen. 
Nervous  system,  high,  senses  well  developed. 

Development  of  nervous  system : 

Protozoa,  direct  to  protoplasm,  sense  heat,  light,  contact. 

Hydra,  special  nerve  cells  in  groups  (ganglia),  motor  control. 

Worms,  ganglia  connected,  beginning  of  brain. 

Crustacea,  fewer  ganglia,  cephalization,  sense  organs. 

Insecta,  very  high  brain  ganglia,  iew  others,  great  motor  control,  instinct. 


204  BIOLOGY  FOR  BEGINNERS 

General  tendency  of  nervous  development: 

1.  Fewer  ganglia. 

2.  Increasing  complexity  (centralizing  control). 

3.  Location  in  anterior  (first  contact  with  environment). 

General  functions  of  nervous  system. 

1.  To  receive  impressions  from  without  (sensation). 

2.  To  control  and  originate  motion  (motor  impulses). 

Life  History: 

1.  Kgg,  fertilized,  buried  in  earth  by  ovipositors. 

20-30  in  two  masses,  in  autumn. 

Functions:   to  reproduce  and  to  pass  winter  protected. 

2.  Nymph,  like  adult  but  small  and  wingless. 

Growth  by  moults,  development  of  wings. 

Complete  and  incomplete  metamorphosis  compared. 
Economic  Importance. 


CHAPTER  XXIV 

INSECTA,   CONTINUED 

Vocabulary 

Vestiges,  remnants  or  traces  of  organs. 

Metamorphosis,  the  series  of  changes  in  the  life  of  an  animal. 

Credible,  believable. 

Communal  life,  life  in  colonies  for  mutual  help. 

Gorged,  filled  with  food. 

Bearing  in  mind  the  fact  that  all  insects  have,  in  general,  the 
same  organs  as  those  found  in  the  grasshopper,  we  shall  now  briefly 
study  how  they  are  developed  in  representatives  of  a  few  other 
insect  orders. 

LEPIDOPTERA 

The  butterflies  and  moths  belong  to  the  order  lepidoptera  (scale 
winged)  and  furnish  a  familiar  type  of  quite  a  different  group  of 
insects. 

Head.  The  antennae  of  butterflies  are  club  shaped  or  knobbed 
at  the  tip  while  those  of  moths  are  usually  feather  like.  The  com- 
pound eyes  are  very  large  and  rounded  and  the  neck  very  flexible, 
but  it  is  in  the  mouth  parts  that  they  differ  most  from  the  or- 
thoptera,  these  being  adapted  for  sucking  nectar  from  flowers. 
The  labrum  and  mandibles  are  reduced  to  mere  vestiges  while 
the  maxillae  are  enormously  lengthened  and  locked  together  to 
form  the  coiled  proboscis  or  tongue  which,  when  extended,  may 
equal  in  length  all  the  rest  of  the  body  and  is  always  long  enough 
to  reach  the  nectar  glands  of  the  flowers  they  prefer.  The  labium 
is  reduced  in  size,  two  feathery  palpi  being  all  that  is  left  of  it  in 
most  cases.  Thus  in  this  set  of  mouth  parts,  we  have  an  example 

205 


206  BIOLOGY  FOR  BEGINNERS 

of  organs  homologous  to  those  of  the  grasshopper,  but  very  differ- 
ently adapted. 

Thorax.  The  legs  of  the  lepidoptera  are  small  and  weak,  having 
the  same  general  structure  as  in  all  insects.  Obviously  the  but- 
terfly neither  walks  nor  jumps.  It  uses  its  legs  only  for  clinging  to 
its  resting  places  and  spends  most  of  its  time  in  the  air.  The 
wings  are  large  and  covered  with  colored  scales  from  which  the 
order  gets  its  name.  These  scales  help  the  few  veins  in  giving 


FIG.  65.    Butterfly. 

Fig.  1.  Side  view  of  head.  —  Note  the  club  shaped  antennae  with  sense  hairs 
at  tip.  . 

The  enormous  eyes  curve  out  so  far  that  vision  is  possible  in  all  directions. 

The  small  organs  below  the  eyes  are  palpi  from  the  labium,  which  are  also 
sense  organs. 

The  partly  uncoiled  "tongue"  is  composed  of  the  two  maxillae,  and  has  a 
roughened  tip  for  opening  the  nectar  glands  of  flowers.  It  is  called  the  pro- 
boscis. 

Fig.  2.  Front  view  of  head.  —  Same  parts  shown  as  mentioned  above  except 
that  the  proboscis  has  been  cut  through  to  show  the  two  maxillae,  joined  edge 
to  edge  with  the  tube  between  them  for  sucking  nectar. 

strength  to  the  wing,  and  in  some  cases  in  color  protection  as  well. 
The  thorax  and  its  muscles  which  move  the  wings  are  not  very 
powerful,  and  the  butterfly,  though  easily  supported  by  its  large 
whig  spread,  is  not  a  swift  flyer. 

Abdomen.  The  abdomen  resembles  that  of  the  grasshopper, 
but  has  fewer  segments,  and  as  in  all  insects  is  the  least  specialized 
body  region. 

Life  History.  The  eggs  of  most  lepidoptera  are  deposited  on 
or  near  the  plant  which  will  be  the  food  of  the  young.  Some  pass 


INSECTA,   CONTINUED 


207 


the  winter  in  this  stage  but  usually  eggs  are 
deposited  in  the  spring  and  partly  develop 
that  same  season. 

The  egg  does  not  hatch  into  a  form  at  all 
resembling   the  adult,  but  instead,  there 
emerges  a  tiny  worm-like  form  called  the 
larva,   which   differs  entirely  in  structure, 
having  no  wings,  nor  compound  eyes,  but 
possessing  several  extra  pairs  of  legs  and 
biting   mouth   parts.     In  fact,  these  and 
other  insect  larvae  are  what  we  often  call 
"  worms,"  which  they  do  somewhat  resem- 
ble in  shape.    However,  they  are  really  one 
step  in  the  development  of  an  insect,  and 
are  vastly  more   complex   than   the   true 
worms.    The  larval  stage  devotes  its  whole 
attention  to  eating,  growing,  and  moulting, 
and  after  about  five  changes  of  clothing, 
it  stops  this  gluttonous  life  in  which  it 
often  does  a  great  deal  of 
harm,    and    goes    into   a 
resting   stage    called   the 
pupa. 

In  butterflies,  when  the 
last  moult  occurs,  a  pupa 
case  or  chrysalis  is  formed 
which  protects  the  insect 
during  its  long  pause.  The 
larva  often  seeks  a  pro- 
tected spot  or  burrows  in 
the  earth  before  this 
change  occurs.  The  moth 
larva,  on  the  other  hand, 
spins  a  wonderful  case  of 
silk,  the  cocoon,  by  which 
it  protects  and  attaches  its  pupa  for  its  period  of  retirement. 


FIG.  66.  Sphinx  moth,  showing  pro- 
boscis; at  left  the  proboscis  is  shown  coiled 
up  on  the  under  side  of  the  head,  the  nor- 
mal position  when  not  in  use.  Large  figure, 
one-half  natural  size;  small  figure,  natural 
size.  From  Kellogg. 


208 


BIOLOGY   FOR  BEGINNERS 


This  pupa  stage  in  which  the  lepidoptera  usually  pass  the  winter, 
is  not  really  a  period  of  entire  rest.    Marvelous  changes  take  place 

which  are  not  well  understood, 
but  this  at  least  is  known,  the 
worm-like  larva  emerges  totally 
changed  both  in  internal  and 
external  structure,  as  the  adult 
butterfly  or  moth. 

Whereas  the  larva's  func- 
tion was  to  eat  and  grow,  the 
adult  eats  only  the  nectar  of 
the  flowers  and  its  life  work 
is  to  produce  or  fertilize  the 
eggs  for  the  next  generation. 

Such  a  life  development, 
consisting  of  distinct  stages, 
is  called  complete  metamor- 
phosis, as  distinguished  from  a 
life  history  of  gradual  changes 
(like  the  grasshopper)  which  is 
called  incomplete  metamor- 
phosis. Complete  metamor- 
phosis is  not  confined  to  the 


FIG.  67.  Diagram  of  wings  of 
monarch  butterfly,  Anosia  plexippus, 
showing  venation,  c,  costal  vein;  s.c., 
subcostal  vein;  r,  radial  vein;  ca,  cubital 
vein;  a,  anal  veins.  In  addition,  most 
insects  have  a  vein  lying  between  the 
subcostal  and  radial  veins,  called  the 
medial  vein.  Natural  size.  From 
Kellogg. 


lepidoptera.  The  bees,  beetles, 
and  flies  all  pass  through 
similar  series  of  changes 
which  can  be  tabulated  as 
follows: 

f  Deposited  near  source  of  food 

I  Period  of  increase  in  number 

f  Period  of  eating  and  growth  (usually  harmful) 

I  Worm,  grub,  or  maggot  stage 

f  Period  of  quiet,  internal  transformation 

\  Usually  pass  winter  in  this  stage 

(  Cocoon  or  chrysalis 
Adult  —  Reproductive  stage 


Egg 


Pupa 


ENSECTA;   CONTINUED 


209 


The  larva  of  the  lepidoptera  is  often  very  harmful  as  it  feeds 
on  man's  crops,  the  multitude  of  so-called  "  worms  "  being  only 
too  familiar  examples.  The  pupa  stage  of  the  silk  moth  furnishes 
us  with  silk  from  the  threads  of  its  cocoon.  The  adults  aid  in 


Courtesy  of  the  A  merican  Museum  of  Natural  History. 

FIG.  68.  This  caterpillar  of  the  monarch  butterfly  is  ready  for  the  meta- 
morphosis. It  hatched  in  late  summer  and  grew  for  two  weeks.  It  stopped 
eating,  chose  a  secure  spot  and  spun  a  small  thick  carpet  of  silk.  It  walked  over 
this  until  the  hind  feet  were  entangled  in  the  silk,  then  it  hung  head  downward, 
motionless.  The  skin  now  loosens,  and  after  twenty-four  hours  splits  over  the 
head.  At  this  stage  the  caterpillar,  by  musuclar  contraction  works  the  skin 
off  upward  into  a  small  shriveled  mass;  then  during  the  few  seconds  longer 
that  it  still  remains  attached  to  the  skin,  it  reaches  out  its  slender  end  and  with 
great  effort  and  force  pushes  it  up  into  the  silk  carpet.  The  whole  process  has 
taken  but  three  or  four  minutes.  Slowly  the  shape  changes,  the  segments  above 
contracting,  the  form  rounding  out;  and  behold  an  emerald-green  chrysalis 
studded  with  golden  spots!  In  two  weeks  the  pattern  of  brown  and  orange 
wings  begins  to  show  through,  finally  the  chrysalis  skin  splits  over  the  head, 
and  the  butterfly  crawls  out. 


210 


BIOLOGY  FOR  BEGINNERS 


the  pollenation  of  flowers,  by  reason  of  their  thirst  for  nectar  and 
their  hairy  bodies  which  carry  the  pollen. 


FIG.  69.  Metamorphosis,  complete  of  monarch  butterfly,  Anosia  plexippus. 
a,  egg  (greatly  magnified);  b,  caterpillar  or  larva;'  c,  chrysalis  or  pupa;  d,  adult 
or  imago.  After  Jordan  and  Kellogg.  Natural  size.  (From  Kellogg.) 

Moths  and  butterflies  are  often  confused,  but  can  be  distinguished 
by  the  following  comparison : 

Butterfly 
Day  flier 

Chrysalis  for  pupa 
Wings  vertical  when  at  rest 
Antennae  knobbed 
Abdomen  slender 


Moth 

Night  flier 
Cocoon  for  pupa 
Wings  held  horizontal 
Antennae  feathery 
Abdomen  stout 


INSECTA,   CONTINUED 
ORDER:    HYMENOPTERA 


211 


The  hymenoptera  (membrane  winged),  which  include  the  bees, 
ants,  and  wasps,  represent  the  most  highly  specialized  type  of 
insect.  In  structure,  instinct,  and  manner  of  life  they  far  excel 
all  their  relatives.  A  complete  account  of  the  doings  of  some  of 
the  higher  forms  makes  a  common  fairy  tale  seem  credible  by 
comparison.  Huxley  said  that  an  ant's  "  brain  "  was  the  most 

/tON£r  BEE. 


yuva   -tmucruitr. 


FIG.  70.    Honey  Bee — Mouth  Parts,  etc. 

Figs.  1  and  2.  Mouth  parts.  —  The  mouth  parts  as  a  whole  are  fitted  for 
biting,  cutting  and  lapping  liquids. 

The  labrum  is  reduced  to  a  small  triangular  organ,  of  slight  importance  except 
as  a  guide  for  the  other  parts. 

The  mandibles  (Md.),  are  powerful,  sharp-edged  jaws  with  which  wax  or 
leaf  material  can  be  cut  and  worked. 

The  maxillse  (Mx.),  are  slender,  pointed  organs  which  can  also  be  used  for 
cutting  and  working  in  wax. 

The  labium  is  the  most  highly  modified  of  the  mouth  parts  (La.),  and  is 


212  BIOLOGY  FOR  BEGINNERS 

used  for  lapping  up  nectar  from  flowers.  For  this  purpose  it  is  long,  slender 
and  flexible,  with  roughened  tip  to  hold  more  liquid.  The  labial  palpi  (L.P.) 
are  attached  at  the  side  and  are  probably  sense  organs. 

As  a  whole  the  bee  mouth  parts  present  a  very  high  example  of  specializa- 
tion, in  which  the  usual  six  parts  are  developed  to  a  condition  little  resembling 
the  typical  condition  in  the  grasshopper. 

Resulting  from  this,  the  bee  can  do  several  different  operations  with  its 
mouth  parts,  while  in  most  cases  they  would  be  fitted  only  for  one,  such  as 
biting  in  the  case  of  the  grasshopper,  or  piercing  in  case  of  the  mosquito. 

Fig.  3.  The  Wings.  —  Attention  is  called  to  the  relatively  small  size  and 
fewness  of  veins  in  the  bee  wings.  This  is  evidence  of  high  specialization  here, 
also,  as  they  are  perhaps  the  most  efficient  flying  'apparatus  possessed  by  any 
insect,  yet  are  comparatively  small  and  light. 

The  few  veins  are  placed  in  exactly  those  regions  where  strain  is  greatest, 
the  wing  muscles  are  powerful,  and  operate  at  a  high  rate  of  speed,  which 
accounts  for  their  small  size. 

The  posterior  pair  bears  a  series  of  hooks  which  may  attach  it  to  the  anterior 
pair,  so  that  both  act  as  one  wing  in  flight,  but  fold  back  separately  when  at 
rest. 

wonderful  piece  of  protoplasm  in  the  world,  and  this  would  apply 
almost  equally  to  several  other  representatives. 

Honey  Bee.  As  an  example  of  this  order  we  shall  study  the 
honey  bee,  since  it  is  a  form  with  which  all  are  familiar.  The  body 
regions  are  very  distinct,  the  head  being  attached  to  the  thorax 
by  a  flexible  neck  and  the  thorax  to  the  abdomen  by  a  slender 
waist.  Each  region  is  highly  developed. 

Head.  The  sensitive,  elbowed  antennae,  the  enormous  compound 
eyes  and  three  simple  eyes  are  easily  seen,  but  the  mouth  parts 
are  very  complicated  and  are  really  a  set  of  tools  by  themselves. 
The  labrum  is  small,  but  the  mandibles  are  developed  into  efficient 
cutting  and  biting  organs.  They  are  used  in  manufacturing  wax, 
leaves,  etc.,  into  cells.  The  maxillae  are  complicated  organs  adapted 
also  for  cutting  and  piercing  as  well  as  aiding  in  the  work  of  the 
labium.  The  labiuni  and  its  palpi  form  a  very  efficient  "  tongue  " 
for  lapping  up  the  nectar  upon  which  they  live. 

Thorax.  The  thorax  is  large,  strong,  and  is  provided  with 
powerful  muscles  which  operate  the  legs  and  wings. 

The  bees  are  notably  swift  and  enduring  flyers  and  their  wings, 
while  small,  are  exquisitely  proportioned  and  operate  at  very  hi.uli 
speed,  producing  the  familiar  hum.  The  anterior  wing  is  much 


INSECTA,   CONTINUED  213 

the  larger  and  the  posterior  wing  may  be  attached  to  it,  in  flight, 
by  tiny  hooks.  Honey  bees  often  wear  out  their  wings  by  constant 
use. 

The  three  pairs  of  legs  are  each  provided  with  special  adapta- 
tions. On  the  anterior  pair  is  found  a  notch  and  comb  through 
which  the  antennae  are  drawn  to  clean  them  of  pollen.  The  middle 
pair  have  a  spine  or  spur  which  is  used  in  transferring  pollen  back 
to  the  hind  legs,  which  are  most  highly  specialized  of  all.  This 
pair  has  one  segment  bordered  with  strong  hairs  to  form  a  basket 
for  carrying  pollen.  The  next  segment  has  a  series  of  combs  for 
handling  it,  and  between  the  two  segments  is  a  movable  notch 
which  is  used  as  a  shear  for  cutting  and  shaping  the  wax. 

Abdomen.  The  abdomen  consists  of  six  segments,  with  ovipositor 
or  sting  at  the  posterior  end.  Between  each  segment  are  glands 
which  secrete  wax  for  comb  making. 

Life  History.  The  life  history  of  the  honey  bee  is  the  best 
example  of  communal  life  and  mutual  help.  Each  member  of  the 
colony  works  for  the  good  of  all,  and  this  unselfish  habit  has 
resulted  in  great  success  as  a  whole,  as  well  as  remarkable  develop- 
ment for  each  individual.  There  are  three  forms  of  bees  in  any 
colony,  the  queen,  drones,  and  workers. 

The  Queen.  The  queen  is  almost  twice  as  large  as  the  worker, 
with  a  long  pointed  abdomen,  but  with  no  pollen  basket  nor  comb, 
her  particular  function  being  the  production  of  eggs  to  continue 
the  colony.  She  may  produce  as  many  as  three  thousand  per  day, 
which  is  twice  her  own  weight.  The  queen  develops  from  an 
ordinary  egg,  but  the  workers  enlarge  the  wax  cell  in  which  it  is 
to  grow  and  feed  the  grublike  larva  with  extra  portions  of  nourish- 
ing food.  This  causes  the  development  of  a  queen,  or  fertile 
female,  instead  of  a  worker,  which  is  a  female  without  the  ability 
to  lay  eggs.  After  being  thus  fed  for  five  days,  the  larva  weaves 
a  silken  cocoon,  changes  to  a  pupa,  and  is  sealed  into  her  large 
waxen  chamber  by  the  workers.  When  the  mature  queen  emerges 
from  her  cell,  she  seeks  out  other  queen  larvae  in  the  colony  and 
kills  them,  or  if  she  finds  another  adult  queen,  they  fight  till  one 
is  killed.  She  never  uses  her  sting  except  against  another  queen. 


214 


BIOLOGY  FOR  BEGINNERS 


After  a  few  days  she  takes  a  wedding  flight  in  the  air,  where  she 
mates  with  a  drone,  or  male  bee.  Then  the  eggs  are  fertilized, 
and  she  returns  to  the  hive  and  begins  her  life  work  of  laying  eggs. 
If  the  workers  prevent  her  from  destroying  the  other  queens,  she 
takes  part  of  the  colony  and  "  swarms  "  out  to  seek  a  home  else- 
where. A  queen  may  live  from  three  to  ten  years. 


PC 


B£E 


FIG.  71.    Honey  Bee  —  Leg  Adaptations. 

Notice  that  in  all  the  legs  there  are  the  same  number  of  segments,  but  dif- 
ferently developed.  This  is  an  excellent  example  of  division  of  labor  or  speciali- 
zation among  homologous  parts. 

The  anterior  leg  has,  at  the  first  tarsal  joint,  a  notch  and  a  movable  spine 
over  it,  so  that  the  antennae  may  be  drawn  through  and  cleaned  of  pollen 
after  visits  to  the  flowers.  When  you  realize  that  the  antennae  are  the  insect's 
most  important  sense  organs,  except  possibly  the  eyes,  this  is  seen  to  be  an 
important  special  function. 

The  middle  leg  is  only  slightly  modified,  but  has  a  strong  spine  which  is  used 


INSECTA,   CONTINUED  215 

in  passing  back  the  pollen  from  the  other  legs  and  depositing  it  in  the  pollen 
baskets. 

The  posterior  leg,  of  which  both  surfaces  are  shown,  is  most  highly  special- 
ized. Along  the  edges  of  the  tibia  are  developed  strong  rows  of  hairs  which 
form  a  pocket  or  basket,  in  which  the  pollen  is  carried. 

The  joint  between  the  tibia  and  the  first  tarsal  segment  is  shaped  like  a  pair 
of  shear  jaws,  and  is  used  for  wax  working. 

The  first  tarsal  segment  is  provided  with  rows  of  stiff  hairs  which  help  to 
comb  the  pollen  into  the  baskets,  or  from  the  opposite  legs. 

The  rest  of  the  tarsal  segments  are  developed  as  usual,  for  clinging  in  loco- 
motion, in  the  case  of  all  three  sets  of  legs. 

In  the  bee,  then,  there  are  at  least  six  different  functions  performed  by  the 
legs,  for  which  they  are  provided  with  special  structural  adaptations. 

Such  high  development  is  probably  the  result  of  the  habit  of  communal 
life  which  permits  greater. division  of  labor  than  is  possible  where  animals  live 
alone  or  in  pairs. 

The  Drones.  The  drone,  while  larger  than  the  worker,  is  smaller 
than  the  queen  and  has  a  thick,  broad  body,  enormous  eyes,  and 
very  powerful  wings.  It  is  not  provided  with  pollen  baskets, 
sting,  or  wax  pockets. 

His  tongue  is  not  long  enough  to  get  nectar,  so  he  has  to  be  fed 
by  the  workers  and  his  sole  function  is  to  fertilize  the  eggs  of  the 
queen.  However,  this  easy  life  has  its  troubles  for  with  the  coming 
of  autumn  when  honey  runs  low,  the  workers  will  no  longer  support 
the  drones,  but  sting  them  to  death,  and  their  bodies  may  be  found 
around  the  hives  in  September. 

The  Workers.  The  workers  are  by  far  the  most  numerous 
inhabitants  of  the  hive;  they  are  undeveloped  females,  smaller 
than  drones  with  the  ovipositor  modified  into  the  sting,  and  with 
all  the  adaptations  of  legs,  wings,  and  mouth  parts,  which  have 
been  described. 

With  the  exception  of  the  process  of  reproduction,  all  the  varied 
industries  and  products  of  the  hive  are  their  business  and  they 
perform,  at  different  times,  many  different  kinds  of  work  as  well 
as  providing  the  three  hive  products  —  wax,  honey,  and  propolis. 
In  summer  they  literally  work  themselves  to  death  in  three  to 
four  weeks,  but  may  live  five  to  six  months  over  winter. 

Products  of  the  Hive.  Wax  is  a  secretion  from  the  abdominal 
segments  of  workers,  which  comes  after  they  have  first  gorged 


216  BIOLOGY  FOR  BEGINNERS 

themselves  with  honey,  and  then  have  suspended  themselves  by 
the  feet  in  a  sort  of  curtain.  As  the  wax  is  produced,  it  is  re- 
moved by  other  workers,  chewed  to  make  it  soft,  and  then  carried 
to  still  others  by  whom  it  is  built  into  comb. 

This  comb  is  a  very  wonderful  structure,  composed  of  six-sided 
cells  in  two  layers,  so  arranged  as  to  leave  no  waste  space,  and 
afford  the  greatest  storage  capacity  with  the  use  of  the  least 
material.  Not  only  is  it  used  for  storage  of  honey,  and  "  bee 
bread  "  (a  food  substance  made  from  pollen  and  saliva)  but  also 
for  the  rearing  of  young  bees,  the  eggs  being  placed  one  in  a  cell 
by  the  queen  and  sealed  up  by  the  workers,  making  what  is  called 
"  brood  comb." 

Honey  is  made  from  the  nectar  of  flowers  which  is  taken  into 
the  crop  of  the  bee,  its  cane  sugar  changed  to  the  more  easily 
digested  grape  sugar,  and  then  emptied  into  the  comb  cells,  where 
it  is  left  to  ripen  and  evaporate  before  being  sealed  up.  Until  the 
seventeenth  century,  people  did  not  know  how  to  make  sugar, 
and  depended  upon  honey  entirely  for  this  necessary  food.  At 
present  the  bee  products  in  United  States  are  worth  $22,000,000 
per  year. 

The  removal  of  honey  by  man  does  not  harm  the  bees  if  about 
thirty  pounds  be  left  for  their  winter  use,  that  being  sufficient  to 
feed  the  average  colony  of  about  40,000  bees  for  an  ordinary  winter. 

Propolis,  or  bee  glue,  is  another  important  product  of  the  hive. 
It  is  gathered  from  the  sticky  leaf  buds  of  some  plants.  Bees  will 
even  use  fresh  varnish  if  they  can  get  at  it.  It  is  used  to  make 
smooth  the  interior  of  the  hive,  to  help  attach  the  comb,  to  close 
up  holes  and  cracks,  and  even  to  varnish  the  comb  if  it  is  left 
unused  for  a  time;  it  is  the  brown  substance  which  may  be  seen 
on  section  boxes  in  the  stores. 

Industries  of  the  Colony.  Not  only  do  the  workers  prepare  the 
wax,  honey,  and  propolis,  as  needed,  but  they  have  other  duties 
as  well,  which  they  also  take  turns  in  performing.  Some  attend 
and  feed  the  queen  or  drones;  some  act  as  nurses  to  the  hungry 
larvae,  which  they  feed  with  partly  digested  food  from  their  own 
stomachs;  some  clean  the  hive  of  dead  bees  or  foreign  matter;  some 


INSECTA,  CONTINUED 


217 


fan  with  their  wings  to  ventilate  the  hive  and,  all  the  time,  thousands 
of  others  are  bringing  in  the  nectar,  pollen,  and  propolis  as  needed 
for  use  of  the  colony.  Such  a  communal  or  colony  life  illustrates 
the  highest  development  of  division  of  labor  found  among  the 
animals  lower  than  man,  and  occurs  among  some  ants  and  wasps 
as  well  as  bees,  though  nowhere  carried  to  a  higher  point  than  in 
the  honey  bee. 

Larval  Forms.  The  larval  forms  of  many  insects  are  so  different 
from  the  adults  that  they  have  received  separate  names  which 
sometimes  confuse  the  relationship. 


The  larva  of  the 


beetle 

fly 

bee   ' 

mosquito 

butterfly 

moth 


is  called  a 


grub 
maggot 
grub 
wiggler 

caterpillar  or  "  worm  " 
(  caterpillar  or  "  worm  " 


We  speak  of  "  silk  worms,"  or  "  apple  worms,"  etc.,  when  we 
really  refer  to  larval  forms  of  moths;  "  cabbage  worms  "  and 
"  currant  worms  "  are  larvae  of  butterflies. 

"  Wire  worms  "  are  beetle  larvae;  the  "  moth  "  that  eats  woolens 
is  the  larva  and  not  the  moth  itself;  the  "  carpet  bug  "  or  "  buffalo 
bug  "  is  the  larva  of  a  beetle. 


COLLATERAL   READING 

Manual  for  the  Study  of  Insects,  Comstock,  pp.  48-76,  104-118;  Insect 
Life,  Comstock,  pp.  11-21;  Guide  for  the  Study  of  Insects,  Packard;  En- 
tomology for  Beginners,  Packard,  pp.  178-223;  Insecta,  Hyatt  and  Arms; 
Elements  of  Zoology,  Davenport,  pp.  11-89;  Animals  and  Man,  Kellogg, 
Chap.  XV;  Textbook  of  Zoology,  Colton,  pp.  1-53;  Lessons  in  Zoology, 
Needham,  pp.  36-104;  Practical  Zoology,  Davison,  pp.  30-125;  Compara- 
tive Zoology,  Kingsley,  pp.  213-234;  Elementary  Zoology,  Galloway,  pp. 
232-273;  First  Book  of  Zoology,  Morse,  pp.  49-108;  General  Zoology,  Lin- 
ville  and  Kelly,  pp.  1-100;  General  Zoology,  Herrick,  pp.  153-195;  Animal 
Life,  Jordan,  Kellogg  and  Heath,  pp.  149-155;  Animal  Studies,  Jordan, 
Kellogg  and  Heath,  pp.  130-149;  Elementary  Biology,  Peabody  and 
Hunt,  pp.  9-61;  Introduction  to  Biology,  Bigelow,  pp.  279-286;  Applied 
Biology,  Bigelow,  pp.  380-398;  Nature  Study  and  Life,  Hodge,  Chap. 


218  BIOLOGY  FOR  BEGINNERS 

V,  X,  pp.  181-294;  Handbook  of  Nature  Study,  Comstock,  pp.  308-451; 
Life  in  Ponds  and  Streams,  Furneaux,  pp.  202-345;  Life  and  Her  Chil- 
dren, Buckley,  pp.  201-268;  Insect  Friends  and  Foes,  Craigin,  pp.  53-76; 
Insect  Life  of  Farm  and  Garden,  Sanderson,  see  index;  Insects  Injurious 
to  Fruits,  Saunders,  see  index;  Injurious  and  Useful  Insects,  Miall,  see 
index;  Insects  and  Insecticides,  Weed,  see  index;  Insects  Injurious  to 
Vegetation,  Chittenden,  see  index;  Insect  Pests  of  Farm  and  Garden, 
see  index;  Insects  Injurious  to  Trees,  N.  Y.  State  Report;  Economic 
Entomology,  Smith,  pp.  11-51,  79-100;  Economic  Zoology,  Osborne,  pp. 
235-310;  Economic  Zoology,  Kellogg  and  Doane,  pp.  14-25,  125-182; 
Life  Histories  of  American  Insects,  Weed,  see  index;  Insect  Book, 
Howard,  pp.  332-346;  Butterfly  Book,  Holland;  Moth  Book,  Holland;  How 
to  Know  the  Butterflies,  Comstock;  Cornell  Leaflets  (bound  volume), 
1894-1904,  pp.  135-140;  Cornell  Leaflets,  pp.  226-261;  Cornell  Leaflets, 
pp.  529-557;  Cornell  Leaflets,  pp.  213-223;  Cornell  Leaflets,  1915,  pp. 
153-190;  Cornell  Leaflets,  1916,  pp.  122-152. 

SUMMARY 

Lepidoptera  (scale  winged)  moths  and  butterflies. 

1.  Structure: 

Head,  antennae,  knobbed  or  feather  shaped. 
Compound  eyes. 

Mouth  parts  (adapted  for  sucking  nectar). 
Labrum  and  mandibles  reduced. 
Maxillae  form  proboscis. 
Labium  reduced  to  palpi. 
Thorax, 

Legs  small  and  weak. 

Wings  large,  few  veins,  scaled,  slow  motion. 
Abdomen, 

Little  specialized. 

2.  Life  history  (complete  metamorphosis): 

Egg  laid  on  food  plants. 

Larva,  caterpillar  (eating  stage),  harmful. 

Pupa,  cocoon  or  chrysalis  (quiet  stage),  silk. 

Adult,  moth  or  butterfly  (reproductive  stage)  pollenation. 

Hymenoptera  (membrane  winged)  bees,  ants,  and  wasps. 
1.   Structure: 

Head,  antennae,  short,  elbowed. 
Eyes  very  large. 

Mouth  parts  (adapted  for  biting,  lapping,  and  sucking). 
Labrum,  small,  triangular. 
Mandibles,  sharp  for  biting. 
Maxillae,  long,  sharp,  for  cutting  wax,  etc. 
Labium,  tongue-like,  for  lapping  nectar. 


INSECTA,  CONTINUED  219 

Thorax,  large  and  strong. 
Wings  small  but  powerful. 
Legs,  anterior  with  antenna  cleaner, 
middle  with  pollen  spine, 
posterior  with  pollen  basket  and  wax  shears. 
Abdomen,  six  segments. 
Ovipositor  or  sting. 
Wax  glands. 

2.  Life  history  (complete  metamorphosis)  communal  life. 

Egg,  laid  by  queen  in  comb  cells. 
Larva,  helpless  grub,  fed  by  workers. 
Pupa,  sealed  in  wax  cell. 
,  Adult,  three  forms  as  follows: 

Queen,  large,  fertile  female,  produces  eggs. 

Drone,  thick  body,  large  eyes,  fertilizes  eggs. 

Workers-,  smaller,  sting  in  place  of  ovipositor. 

3.  Hive  products: 

Wax,  secreted  from  abdominal  segments  of  workers. 
Honey,  concentrated  and  partly  digested  nectar. 
Propolis,  glue  made  from  plant  gums.     "  Bee  bread." 

4.  Division  of  labor  (among  workers). 

Collection  of  nectar,  pollen  and  gum. 

Preparation  of  wax,  honey,  propolis,  and  bee  bread. 

Feeding  queen,  drones,  and  larvae. 

Ventilating  hives  by  fanning,  cleaning  hives. 

Guarding  hives  from  intruding  insects  and  robber  bees. 


CHAPTER  XXV 

INSECTS  AND   DISEASE 
FLIES  AND  MOSQUITOES 

Vocabulary 

Excrement,  waste  matter  thrown  off  by  animals  from  the  intestine 

or  kidneys. 

Cooperation,  working  together  for  a  single  purpose. 
Invariably,  always,  without  exception. 
Contract,  to  "  take"  a  disease. 

Another  insect  order  which  we  shall  take  up  very  briefly  is  the 
diptera  (two-winged)  which  includes  the  flies  and  mosquitoes. 
They  are  studied  chiefly  because  of  their  relation  to  the  carrying 
of  disease  germs.  The  diptera  differ  from  all  other  insects  by 
having  but  one  pair  of  wings,  the  posterior  pair  being  replaced  by 
flat  or  knob  shaped  balancers.  Their  mouth  parts  are  fitted  for 
piercing,  rasping,  and  sucking,  and  their  metamorphosis  is  complete. 

The  Typhoid  Fly.  The  common  house  fly  (typhoid  fly)  has  very 
highly  developed  mouth  parts  adapted  for  rasping  and  sucking, 
large  eyes,  and  short  fleshy  antennae.  Its  wings,  though  but  two 
in  number,  are  well  developed,  and  operated  at  high  speed  by  the 
powerful  muscles  of  the  thorax;  the  posterior  pair  are  replaced  by 
flattened  balancers.  The  six  legs  are  well  developed  and  the  feet 
(tarsi)  are  provided  with  claws  and  sticky  hairs  which  aid  in  loco- 
motion. Unless  these  hair  tips  are  very  free  from  dust  they  will 
not  stick  well  and  the  fly  cannot  walk  readily  on  smooth  surfaces, 
hence  the  care  with  which  it  cleans  its  feet  by  constantly  rubbing 
them  against  each  other  and  its  body. 

Life  History.  However,  our  principal  concern  is  with  the  life 
history  and  habits  of  the  fly  rather  than  with  its  structure,  since 
it  is  in  this  connection  that  it  affects  man's  health. 

220 


INSECTS  AND   DISEASE 


221 


The  eggs  are  deposited  in 
horse  manure  if  it  is  to  be 
found,  or  in  other  similar 
matter,  about  two  hundred 
being  laid  by  each  female. 
They  hatch  in  one  day  into 
the  larval  form  which  we  call 
maggots,  and  in  this  stage 
do  some  good  as  scavengers. 
After  eating  and  growing  for 
about  five  or  six  days,  the 
larvae  pass  into  the  pupal 
condition,  inside  the  last  lar- 
val skin,  which  thus  takes 
the  place  of  a  cocoon.  From 
this  the  adults  emerge  in 
about  a  week.  The  whole 
process  occupies  about  two 
weeks,  begins  early  in  spring, 


American  Museum  of  National  History 
FIG.  73.     Eggs  of  the  housefly. 


Courtesy  of  the  American  Museum  of  Natural  History 
FIG.  72.     Common  house  (typhoid)  fly. 

and  continues  till  cold 
weather.  Supposing  that 
half  the  eggs  produced  fe- 
males and  these  reproduce 
at  the  same  rate,  calculate 
the  number  of  flies  that 
might  be  produced  by  one 
adult  which  had  survived  the 
winter,  and  the  enormous 
number  of  flies  in  existence 
will  be  accounted  for. 

Danger  from  Flies.  Flies 
have  always  been  regarded  as 
more  or  less  of  a  nuisance,  as 
they  crawl  over  our  food  and 
our  bodies,  fall  into  milk  and 
other  liquids,  and  annoy  man- 


222  BIOLOGY  FOR  BEGINNERS 

kind  in  various  ways,  but  their   real  harm  has  only  recently 
been  realized. 

They  live  in  and  feed  upon  manure  and  filth,  then  come  and 
crawl  over  our  food  and  faces,  or  wash  themselves  in  the  cream 
pitcher.  When  we  realize  that  typhoid,  cholera,  and  dysentery  are 
intestinal  diseases,  that  the  germs  are  carried  off  by  the  excrement 
in  which  flies  thrive,  it  is  no  wonder  that  they  infect  our  food  when 


FIG.  ?4.   Larvae  and  pupae  of  housefly,  Musca  domestica,  in  manure.  Natural 
size.     From  Kellogg  and  Doane. 

they  crawl  upon  and  share  it  with  us.    The  fly  is  not  only  a  filthy 
but  a  very  harmful  insect  and  one  to  be  avoided  and  destroyed. 

A  fly  eats  its  own  weight  of  food  every  day.  Its  food  is  largely 
manure,  sputum,  and  other  filth,  though  it  also  samples  our  food 
at  table.  Disease  germs  pass  through  the  fly's  intestine  unharmed 
and  remain  active  in  the  familiar  "  fly  specks  "  which  are  deposited 
at  intervals  of  five  minutes.  Thus  the  fly  carries  filth  and  disease 


INSECTS  AND  DISEASE 


223 


both  externally  on  its  feet  and  body  and  internally  by  way  of  its 
food  and  excreta. 

Our  common  flies  transmit  typhoid,  cholera,  summer  complaint, 
dysentery,  tuberculosis,  and  probably  other  diseases  where  the 
germs  pass  from  the  body  in  any  form  of  excrement,  pus,  or  sputum. 
The  tsetse  fly  of  Africa  transmits  the  deadly  "  sleeping  sickness." 
Thus  it  is  seen  that  flies  which  we  formerly  regarded  as  an  un- 


FIG.  75.    Foot  of  housefly  showing  claws,  hairs,  pulvillae  and  the  minute 
clinging  hairs  on  the  pulvillae.     From  Kellogg  and  Doane. 

avoidable  nuisance,  have  been  proven  to  be  responsible  for  the 
death  of  more  people  than  all  wild  beasts  and  reptiles  together, 
and  that  actually  they  are  more  dangerous  to  man  than  the  tiger, 
grizzly,  or  rattlesnake. 

Rate  of  Reproduction.  In  the  face  of  its  enormous  rate  of  in- 
crease, "  swatting  "  of  individual  flies  is  a  losing  battle  as  the 
following  figures  show.  Supposing  that  reproduction  was  un- 
checked and  that  all  offspring  survive  (which  fortunately  is  not 


224  BIOLOGY  FOR  BEGINNERS 

always  the  case)   then  one  fly  would  produce  in  the  different 
generations  of  two  weeks  each  as  follows. 

1st  200  (half  females) 

2nd      (100x200)  20,000  (  "         "     ) 

3d   (10,000x200)  2,000,000 

4th  200,000,000 

5th  20,000,000,000 

6th  2,000,000,000,000 

2,020,202,020,200  total  in  12  weeks 

or  the  perfectly  unthinkable  number  of  over  two  million  millions 
in  half  the  breeding  season,  which  would  be  over  20,000  flies  to 
be  killed  by  each  man,  woman,  or  child  in  the  United  States  - 
and  this  the  progeny  of  one  adult  female  which  survived  the  winter. 
Fly  Control.  Fortunately  there  are  more  efficient  ways  of  de- 
stroying this  dangerous  pest.  These  are  briefly  tabulated  below: 
government  bulletins  fully  describing  all  methods  may  be  had  for 
the  asking,  and  general  cooperation  has  much  reduced  the  pest 
in  many  cities.  The  following  are  the  most  efficient  methods  of 
control : 

1.  Horse  manure  and  other  filth  can  be  removed,  screened,  or 

chemically  treated  to  kill  the  larvae. 

2.  Garbage  and  sewage  can  be  properly  covered  and  removed. 

3.  Houses  can  be  screened. 

4.  Food,  especially  in  stores,  can  be  protected. 

5.  Fly  traps  and  wholesale  poisons  are  helpful. 

The  Mosquito.  The  mosquito  is  another  member  of  the  diptera 
which  demands  mention  because  it,  too,  transmits  serious  diseases 
to  man  though  it  acts  in  a  different  way  from  the  fly.  The  germs 
actually  develop  a  part  of  their  life  history  within  the  mosquito's 
body,  while  the  fly  merely  carries  its  dangerous  burden, 
mechanically. 

Mouth  Parts.  In  the  mosquito,  the  labrum,  tongue,  mandibles, 
and  maxillae  are  reduced  to  sharp,  lance-like  bristles,  enclosed 
within  the  labium  as  a  sheath,  and  are  adapted  for  piercing  and 
sucking.  In  order  to  dilute  the  blood,  so  that  they  can  withdraw 


INSECTS  AND   DISEASE 


225 


it,  they  inject  a  little  saliva,  which  causes  the  usual  irritation  and 
swelling  of  a  mosquito  bite. 
Disease  Transmission.    This  would  be  bad  enough,  but  it  has 


SOURCE 
Nasal  discharges 
Open  sores 


DISEASE       HOW  ENTERS  MAN 


Carcasses 
Sputum 

Privies   1 
Manure} 


infantile  paralysis 

optha/mia 

syphi/is 

yaws 

anthrax 


faberca/osis 
typ/io/d 

diarrhoea 
Cfio/era 

tapeworm 


Open  jore 
rood 


SWAT  THE: 

FIRST 
FLY 


2S9Z0OOO 


rfy  lays  /ZO  e0QS 

MAY  10.  60  Hits  lay 
MAYZO.  3600  Hies  fay 
MAY3O.ZI6OOO  F/itt  /ay 
JUNE  /O.  I Zf 60000  Hie*  /ay 

JUA/EZO-77000O00  Flies  lay          933/2.0O00O0  e<&S 
"JUME  30-304665600000  f/tes  /ay         JS987Z00OO000  e&S 
=JULY  9-  279 9 J6 0000000 r/ies  /ay    3ZS9Z3ZOOOOOO00  e<?&S 
JULY  1 1- 167^6/600000000  Flies  lay  2O/ SSJ9&OO  OOOOOOO  eggS 

JUL  Y  2cl-/00'r  76  <3600O0o0OOO  Flies  lay  /1093ZJ  JX.00O0006OOO  e#0S 

AUGUST  S-60466/760000O0OOO0Flie3  lay  7'£<3'>5e:i4/l2O00OO0O0000  Sf&S 

FIG.  76. 

Upper.  —  Diagram  showing,  the  relation  of  flies  to  disease. 
Lower.  —  Cartoon  from  newspaper  showing  rate  of  increase  of  the  fly. 
From  Pearse. 

been  absolutely  proven  that  if  certain  species  of  mosquitoes  bite 
a  person  having  either  malaria  or  yellow  fever,  the  protozoan 
which  causes  the  disease,  is  taken  up  with  the  blood,  develops  in 
the  mosquito's  body  and  may  be  injected  with  the  saliva  into  the 


226 


BIOLOGY  FOR  BEGINNERS 


blood  of  a  well  person.  Not  only  has  this  been  shown,  but  by  means 
of  experiments  in  which  several  men  sacrificed  their  lives,  it  is  also 
proven  that  this  is  the  only  way  in  which  these,  and  probably 
other  diseases,  are  transmitted.  Men  tended  yellow  fever  patients, 
slept  hi  their  beds,  wore  their  clothes  and  though  exposed  hi  every 
way,  did  not  contract  the  disease  as  long  as  screened  from  mos- 
quitoes. Others  who  allowed  themselves  to  be  bitten  by  mos- 
quitoes which  had  previously  bitten  yellow  fever  patients,  in- 
variably contracted  the  disease,  which  in  some  cases  resulted  in 
their  death.  From  these  sacrifices,  methods  of  control  have 


FIG.  77.    Mass  of  mosquito  eggs. 

developed  which  have  saved  thousands  of  lives  in  all  parts  of  the 
world. 

Life  History.  As  with  the  fly,  a  knowledge  of  its  life  history 
enables  man  to  contend  with  the  mosquito,  and  these  campaigns 
are  much  more  successful  than  those  against  the  fly.  The  eggs 
are  laid  in  stagnant  water;  ponds,  rain  barrels,  and  even  tin  cans 
furnish  ideal  breeding  places.  They  are  deposited  in  tiny  rafts, 
consisting  of  many  eggs  covered  with  a  waterproof  coating,  and 
when  they  hatch  the  larvae  emerge  downwards  into  the  water, 
and  become  the  familiar  "  wigglers  "  seen  in  rain  barrels.  Though 
living  in  water  the  mosquito  larva  breathes  air,  which  it  obtains 
through  a  tube,  projecting  from  the  posterior  of  its  abdomen. 
It  may  often  be  seen  with  this  tube  at  the  surface  and  the  body 


INSECTS  AND   DISEASE 


227 


hanging  head  downwards  in  the  water.  The  pupa  stage  is  also 
passed  in  the  water  and  differs  from  most  insect  pupas  in  being 
an  active  "  wiggler  "  as  well  as  the  larva.  It  differs  from  this  larva 
in  having  a  large  head  provided  with  two  air  tubes  for  breathing. 
The  adult  emerges  from  the  floating  pupa  skin  and  is  easily  killed 
by  any  shower  that  wets  its  unexpanded  wings,  or  any  spray  that 
may  be  thrown  upon  it. 
Our  commonest  northern  mosquito  (culex)  probably  does  not 


\ 


FIG.  78.  Mosquito  eggs  and  larvae  (Theobaldin  incident);  two 
larvae  feeding  on  bottom,  others  at  surface  to  breathe. 
From  Doane. 


transmit  disease  and  may  be  distinguished  from  anopheles,  which 
carries  malaria,  by  the  fact  that  the  latter  stands  almost  on  its 
head  when  at  rest,  while  culex  holds  its  body  more  nearly  hori- 
zontal. Fortunately,  stegomyia  which  transmits  yellow  fever, 
is  a  tropical  species  of  mosquito  and  does  not  usually  invade  the 
temperate  regions. 

Mosquito  Control.    This  outline  of  the  metamorphosis  gives  the 
key  to  the  methods  of  attack  which  consist  of: 


228  BIOLOGY   FOR  BEGINNERS 

1.  Drainage  of  swamps,  covering  or  removal  of  rain  barrels, 

cisterns,  cans,  or  any  hollows  where  water  may  accumulate. 

2.  Spraying  swamps  and  ponds  with  petroleum  which  covers 

the  water  with  a  film  of  oil  so  that  neither  larva  or  pupa  can 
breathe,  and  also  kills  any  adults  which  it  strikes,  though 
this  oil  treatment  is  injurious  to  plants  and  fishes  in  the 
water  thus  treated. 


FIG.  79.    Mosquito  larvae  and  pupae,  T.  incidens,  with  their  breath- 
ing-tube at  the  surface  of  the  water.    From  Doane. 

3.  Fish  and  dragon  flies  are  natural  enemies  of  mosquitoes  and 

should  be  encouraged. 

4.  Careful  screening  of  houses  and  wearing  of  protective  clothing 

especially  in  infected  regions  is  a  helpful  precaution. 

5.  Persons  suffering  from  malaria  should  avoid  being  bitten 

lest  they  thus  infect  others.    Yellow  fever  cases  are  now 
quarantined  in  screened  rooms  for  the  same  reason. 


INSECTS  AND  DISEASE  229 

By  such  methods  both  malaria  and  yellow  fever  have  been 
stamped  out  in  many  regions  formerly  very  dangerous.  The  chief 
obstacle  to  the  completion  of  the  Panama  Canal  by  the  French 
was  the  awful  death  rate  due  to  these  diseases.  Now,  with  proper 
sanitary  measures,  the  canal  zone  has  a  lower  death  rate  than 
New  York  City.  Because  of  the  modern  knowledge  of  disease 
transmission  and  control  as  applied  by  Colonel  W.  C.  Gorgas, 
the  completed  canal  stands  as  a  monument  to  American  health 
science  as  well  as  to  American  engineering.  The  consequences  of 
heroic  experiment  have  been  far  reaching  in  other  notable  plague 
spots.  Central  America,  West  Indies,  and  the  Philippines  are 
now  healthful  regions.  New  Orleans,  formerly  scourged  by  epi- 
demics of  yellow  fever,  is  now  almost  free  from  this  dreadful  malady. 

A  Biologic  Victory.  One  of  the  most  brilliant  chapters  in  the 
history  of  the  war  against  disease  recounts  the  work  of  four  Ameri- 
can Army  Surgeons  in  the  conquest  of  yellow  fever. 

In  1900,  Doctors  Reed,  Carrol,  Lazear,  and  Agramonte  were 
sent  to  Cuba  to  study  this  disease  which  had  always  been  a  scourge 
in  the  West  Indian  region  and  was  now  spreading  among  our 
soldiers.  They  suspected  a  certain  kind  of  mosquito  as  the  carrier, 
but  could  not  test  their  theory  on  animals,  as  only  human  beings 
have  yellow  fever.  So  they  decided  to  try  it  on  themselves,  and 
allowed  mosquitoes,  which  had  bitten  yellow  fever  patients,  to 
bite  them  and  infect  them  with  the  deadly  germs.  Carrol  was  the 
first  to  be  ill,  but  after  a  long  and  painful  sickness,  finally  recovered. 
Lazear  was  the  next  to  come  down  with  the  disease  and  he  died 
Still  the  experiments  went  on,  despite  the  terrible  risk,  and  there 
were  many  new  volunteers.  Two  others  were  selected,  a  soldier, 
Kissenger,  and  a  civilian,  Moran.  Both  insisted  that  they  receive 
no  pay,  as  they  willingly  offered  their  lives  for  the  benefit  of 
humanity.  Both  men  recovered  after  severe  illness,  but  Kissinger 
was  permanently  disabled  as  the  result  of  his  heroism. 

Based  on  the  work  of  this  gallant  band  of  soldiers  of  science, 
they  were  able  to  prove  that  the  mosquito  was  the  only  carrier  of 
yellow  fever,  and  to  propose  means  for  its  control.  An  active 
campaign  was  begun  at  once  and  in  1901  only  eighteen  deaths 


230  BIOLOGY  FOR  BEGINNERS 

occurred  in  Havana  and  none  at  all  in  1902.  The  terrible  curse 
of  the  tropics  was  wiped  out. 

Major  Reed  writes  "  In  my  opinion  this  exhibition  of  moral 
courage  has  never  been  surpassed  in  the  Army  of  the  United 
States." 

The  history  of  medicine  and  sanitation  is  full  of  such  examples 
of  quiet  heroism,  where  men  have  offered  themselves  to  suffering 


FIG.  80.    A  female  mosquito,  T,  incidens;   note  the  thread-like 
antennae.    From  Doane. 

and  death  far  worse  than  is  incurred  in  battle  and  without  the 
excitement  of  war  or  the  encouragement  of  popular  applause. 

The  conquest  of  malaria  was  brought  about  in  similar  manner, 
by  the  careful  research  and  courageous  experiment  of  English 
and  Italian  doctors.  As  late  as  1894  the  Standard  Dictionary  of 
Medicine  said  that  malaria  was  caused  by  "an  earth-born  poison 
generated  in  the  soil  "  and,  as  its  name  signifies,  was  associated 
with  bad  air  especially  night  air. 


INSECTS  AND  DISEASE  231 

The  malaria  germ  had  been  seen  by  a  French  surgeon  in  1880, 
but  not  associated  with  mosquitoes  at  all,  though  in  1884  an 
American,  A.  F.  A.  King,  had  urged  this  as  possible.  In  1897 
two  English  physicians,  Manson  and  Ross,  traced  the  germ  of 
bird  malaria  to  the  mosquito  and  the  following  year  two  Italians, 
Grassi  and  Bignami,  found  the  germ  of  human  malaria  in  the  body 
of  mosquitoes. 

By  experiments  similar  to  those  described  for  yellow  fever,  it 


FIG.  81.    A  male  mosquito,  T.  incident;  note  the  feathery  antennae. 
From  Doane. 


was  proven  possible  to  live  in  health  in  the  worst  swamps  of  the 
Roman  Campagna,  if  protected  from  mosquitoes.  To  finally 
prove  their  action  in  malaria  transmission,  Doctor  Manson's  son 
and  another  volunteer  were  inoculated  with  malaria  by  mos- 
quitoes brought  from  Italy.  Both  took  the  disease,  but  fortunately 
were  cured.  It  is  to  such  work  as  this  that  science  owes  her  victories 
and  to  it  we  owe  also  our  greater  safety  from  disease. 


232 


BIOLOGY  FOR  BEGINNERS 
SOME  MEANS  or  DISEASE  TRANSMISSION 


Disease 

Transmitted  by 

Means  of  prevention 

Malaria 

Mosquito 

Drainage  and  oiling  of  swamps 

• 

Screening  and  isolation  of  patients 

Yellow  fever 

Mosquito 

As  above 

Typhoid  fever 

Flies 

Destroy  breeding  places 

Kill  breeding  females  in  spring 

Screen  food  and  waste 

Tuberculosis 

Flies 

As  above 

Dysentery 

Flies 

Spotted  fever 

Ticks 

Destruction  of  insect  pest 

Cattle  fever 

Ticks 

Cleanliness 

Relapsing  fevers 

Lice 

Cleanliness,  destruction  of  pests 

Bedbugs 

Sleeping  sickness 

Tsetse  fly 

Protection  against  fly  attack 

The  "Plague" 

Fleas  on  rats  and 

Destruction  of  rodent  hosts 

squirrels 

COLLATERAL   READING 

Principles  of  Health  Control,  Walters,  pp.  347-369;  Civic  Biology, 
Hunter,  pp.  217-231;  Economic  Zoology,  Kellogg  and  Doane,  pp.  349-385; 
General  Zoology,  Linville  and  Kelly,  pp.  284-287;  Town  and  City,  Jewett, 
pp.  228-241;  Primer  of  Sanitation,  Ritchie,  pp.  145-150,  103-116;  Applied 
Biology,  Bigelow,  pp.  282-286;  Mosquitoes  or  Man,  Boyce,  pp.  204-210; 
Protozoology,  Calkins,  pp.  279-285;  Essentials  of  Biology,  Hunter,  pp.  258- 
260;  The  House  Fly,  Howard,  entire;  Civic  Biology,  Hunter,  pp.  217-226; 
Lab.  Problems  in  Civic  Biology,  Hunter,  pp.  149-157;  Sanitation  Practically 
Applied,  Wood,  pp.  420-444;  Community  Hygiene,  Hutchinson,  pp.  220- 
232;  Scientific  Features  of  Modern  Medicine,  Lee,  pp.  79-85;  Rural  School 
Leaflet  (Cornell),  Vol.  IX,  pp.  184-186;  Bulletin  No.  74  Mississippi  Exp. 
Station,  entire;  Numerous  other  Government  Bulletins. 

See  also  references  in  encyclopedia  or  any  textbook  index  on, 


Flies 

Mosquitoes 
Fleas 
Protozoa 


Etc.,  etc. 


Typhoid  fever 
Malaria 
Yellow  fever 
Bubonic  plague 


INSECTS   AND   DISEASE  233 

SUMMARY 

Reason  for  study  of  diptera. 
Characteristics  of  diptera. 

One  pair  of  wings,  balancers,  complete  metamorphosis. 
Mouth  parts  for  rasping  and  sucking  (fly). 
Mouth  parts  for  piercing  and  sucking  (mosquito). 
Fly. 

Mouth  parts  for  rasping  and  sucking,  large  eyes. 

Thick  fleshy  antennae,  powerful  wings,  sticky  feet,  hairy. 

Life  History. 

Egg,  laid  in  manure  or  filth,  200,  hatch  in  one  day. 

Larva,  maggot,  scavengers,  period:  5-6  days. 

Pupa,  passed  in  last  larva  skin,  period:  7  days. 

Adult,  develop  in  two  weeks  all  summer  (compute  numbers). 
Harm  done  by  flies. 

Annoyance  to  people  and  animals. 

Transfer  filth  to  food. 

Transfer  germs  externally  and  internally. 

Typhoid,  cholera,  dysentery,  tuberculosis,  sleeping  sickness. 
Methods  of  control  or  prevention. 

Cover  manure  Remove  garbage  Use  screens 

Cover  foods  Use  traps  "  Swat  'em  " 

Mosquito. 
Structure. 

Mouth  parts  for  piercing  and  sucking,  saliva  injected. 

Mandibles,  maxillae,  labrum,  and  tongue  inside  labium. 
Relation  to  disease. 

Malaria  and  yellow  fever.  How  proven. 

How  transmitted. 
Life  History. 

Egg,  in  rafts  on  the  water. 

Larva,  wigglers,  breathe  head  downwards. 

Pupa,  also  active,  breathe  head  upwards. 

Adult,  female  bites  animals,  male  harmless. 
Control  and  prevention. 

Drainage  of  swamps.  Spraying  with  oil. 

Fish  and  dragon  flies.  Screening  houses. 

Protecting  those  who  are  sick. 
Kinds. 

Culex,  common  northern  mosquito,  body  horizontal. 

Anopheles,  malaria,  body  almost  vertical. 

Stegomyia,  yellow  fever,  tropical. 


CHAPTER  XXVI 

INTRODUCTION   TO  THE  VERTEBRATES 

Vocabulary 

Specialization,  development  of  parts  for  special  function. 

Survival,  remaining  alive. 

Ultimate,  furthest. 

Vertebrates,  animals  having  a  back  bone  composed  of  vertebrae. 

While  it  is  certain  that  all  living  things  are  more  or  less  related 
to  each  other,  still  they  have  developed  along  very  different  lines, 
and  to  very  different  extents. 

Among  animals,  the  protozoa  seem  to  have  carried  the  specializa- 
tion of  the  single  cell  about  to  its  limit,  which,  while  assuring  their 
survival,  could  not  possibly  raise  them  very  high  in  the  scale  of 
development. 

The  sponges  have  obtained  the  utmost  possible  advantage  from 
colonizing  slightly  specialized  cells  in  unspecialized  bodies;  and 
have  attained  a  considerable  advance  over  the  protozoa. 

The  hydra  and  its  relations  reached  a  much  higher  plane  by 
development  of  tissues  for  special  purposes  and  among  them  first 
appear  the  three-layered  body  wall  from  which  the  organs  in  higher 
animals  are  derived. 

The  worms  mark  a  very  diverse  class  but  some  of  them  have 
well-developed  systems  of  organs,  digestive,  circulatory,  nervous, 
etc.,  which  had  never  appeared  in  previous  forms. 

Diverging  from  the  worm  type  it  seems  as  if  nature  had  tried 
out  several  schemes  of  development,  carrying  each  to  a  point  where 
it  could  no  longer  be  much  improved. 

The  molluscs  represent  the  ultimate  advantage  to  be  gained 
from  a  protective  shell  and  rather  high  internal  development, 

234 


INTRODUCTION  TO  THE  VERTEBRATES 


235 


coupled,  in  most  cases,  with  an  inactive  life.    This  made  for  safety 
first,  but  limited  increase  in  activity  and  intelligence. 

The  arthropods,  especially  the  insect  class,  tried  what  could  be 
done  with  an  external  protective  skeleton,  but  one  provided  with 
joints,  so  that  activity  need  not  be  sacrificed  to  safety.  This  has 
produced  the  winners  in  life's  race,  if  numbers  be  the  standard. 


FIG.  82.    Showing  endo-  and  exo-skeletons. 

The  bones  in  a  man's  leg  are  surrounded  by  muscles;  the 
skeleton  of  a  grasshopper's  leg  consists  of  tubes  with  muscles 
inside.  From  Pearse. 

But  the  external  skeleton  and  the  ventral  nervous  system  imposed 
obstacles  to  large  increase  in  size,  on  the  one  hand,  and  to  a  highly 
developed  brain,  on  the  other. 

A  third  line  of  development,  with  the  internal  skeleton  and  the 
nervous  system  dorsal  in  the  body,  was  attempted  by  the  group 
of  animals  called  the  vertebrates.  This  permitted  great  increase 
in  size  both  of  body  and  brain,  and  while  giving  less  protection, 


236  BIOLOGY  FOR  BEGINNERS 

this  very  fact  necessitated  an  active  and  intelligent  life  to  oppose 
or  escape  their  enemies.  The  vertebrates  thus  have  come  to  be 
the  highest  in  the  scale  of  animal  development  and  include  the 
following  classes: 

1.  The  Pisces  (fishes). 

2.  The  Amphibia  (frogs,  toads,  salamanders). 

3.  The  Reptiiia  (snakes,  turtles,  lizards). 

4.  The  Aves  (birds). 

5.  The  Mammals  (rat,  cattle,  cat,  man,  etc.). 

The  vertebrates  include  many  very  different  animals,  but  they 
all  agree  in  the  following  points,  in  which  they  also  differ  from  all 
the  other  forms  studied.  These  other  forms  are  sometimes  all 
classed  together  as  the  invertebrates. 

All  vertebrates  have, 

1.  An  internal  skeleton  of  bone  or  cartilage. 

2.  A  spinal  column  composed  of  vertebrae. 

3.  A  dorsal  nervous  system. 

4.  Two  body  cavities:  a  dorsal  one  for  the  nervous  system  and 

a  ventral  one  for  the  other  organs. 

5.  Eyes,  ears,  and  nostrils  always  on  the  head. 

6.  Jaws,  not  modified  limbs;  move  up  and  down. 

7.  Eyelids  and  separate  teeth  are  usually  present. 

8.  The  heart  is  ventral  and  blood  is  red. 

9.  Never  more  than  two  pairs  of  limbs. 

The  human  body  is  a  true  vertebrate  type  as  we  can  see  by 
comparing  its  structure  with  the  above  points  and  we  only  hold  our 
place  in  the  race  of  life  by  our  superior  brain  development.  There 
is  not  one  of  the  lower  groups  but  has  members  which  excel  us  in 
other  respects. 

Compare  our  swimming  with  the  fish,  our  flight  with  the  bird, 
or  our  speed  with  the  deer  and  it  will  be  seen  that  we  are  inferior 
in  many  respects  to  the  different  members  of  the  animal  kingdom. 
It  is  the  development  of  our  brain  that  has  enabled  us  to  retain 
the  lead  in  the  race  of  life.  Superior  intelligence  compensates 
many  times  over  for  various  physical  disadvantages. 


INTRODUCTION  TO  THE  VERTEBRATES      237 

Here,  as  everywhere  in  Nature,  we  can  see  increase  in  com- 
plexity, permitting  greater  division  of  labor,  and  this  in  turn 
resulting  in  better  adaptation  and  more  perfect  performance  of 
function. 

If  we  compare  the  protozoan  to  the  man  on  the  desert  island, 
then  the  sponge  would  represent  a  condition  where  there  were 
enough  men  (cells),  so  that  one  could  do  one  thing  and  one,  another. 
It  would  be  like  a  small  village  where  one  man  could  make  all  the 
shoes,  or  do  all  the  baking. 

In  the  hydra  we  find  groups  of  similar  cells  (tissues)  performing 


CROSS-SECTIONS 

VCRTE-BRATI 


FIG.  83.     Note  differences  in  location  of  similar  organs  of  vertebrate 
and  invertebrate. 


a  single  function.  This  would  correspond  to  the  case  where  the 
town  had  grown  large  enough  so  that  many  shoemakers  or  bakers 
were  required  and  they  each  worked  together,  as  in  a  factory. 

Worms  and  higher  forms,  with  their  tissues  grouped  into  organs, 
would  correspond  to  larger  cities  where  many  kinds  of  factories 
were  required  to  carry  on  the  business  of  the  still  larger  group  of 
people. 

COLLATERAL   READING 

Applied  Biology,  Bigelow.  pp.  417-419;  Animal  Studies,  Jordan, 
Kellogg  and  Heath,  pp.  161-169;  Economic  Zoology,  Kellogg  and  Doane, 
pp.  237-240;  Winners  in  Life's  Race,  Buckley,  pp.  1-19;  Animal  Life, 
Thompson,  pp.  248-272;  Comparative  Zoology,  Kingsley,  pp.  127-156;  Zo- 
ology, Shipley  and  MacBride,  p.  306;  Elementary  Zoology,  Davenport, 
pp.  289-297;  Elementary  Zoology,  Galloway,  pp.  274-280. 


238 


BIOLOGY  FOR  BEGINNERS 


SUMMARY 
Development  of  the  branches  of  the  Animal  Kingdom. 


Branch.     Examples  (in  notes) 

Protozoa 

Sponges 

Hydra 
Worms 
Molluscs 

Arthropods 


Vertebrates 


Line  of  development. 

Specialized  single  cells. 

Groups  of  slightly  specialized  cells. 

Larger  size,  colonial  habit. 

Three-layered  body  wall,  tissues. 

Systems  of  organs,  sense  organs. 

Protection,  inactive,  low  intelli- 
gence. 

Jointed  exo-skeleton,  active. 

High  developed  senses  and  in- 
stinct. 

Size  and  brain  development  lim- 
ited. 

Internal  skeleton. 

No  limit  to  size  of  brain. 

Less  protected  but  more  intelli- 
gent. 


Classes  of  vertebrates 

Pisces 

Amphibia 

Reptilia 

Aves 

Mammals 
Characteristics  of  vertebrates 

Spinal  column 

Internal  skeleton 

Dorsal  nervous  system. 

Two  body  cavities 

Two  pairs  of  limbs  or  fewer. 


Representatives 

Fishes, 

Frogs,  toads,  salamanders. 

Snakes,  turtles,  lizards. 

Birds. 

Rat,  cow,  cat,  man. 

Sense  organs  on  head. 
Jaws  not  developed  from  limbs. 
Eyelids,  separate  teeth. 
Ventral  heart,  red  blood. 


CHAPTER    XXVII 

FISHES 

Vocabulary 

Aquatic,  pertaining  to  the  water. 

Cartilaginous,  made  of  cartilage,  a  gristle-like  tissue. 

Nasal,  pertaining  to  the  nose. 

Operculum,  the  covering  over  the  gills  in  fishes. 

Filaments,  any  thread-like  organs. 

Prehension,  the  function  of  grasping. 

Visceral,  pertaining  to  the  viscera  or  abdominal  organs. 

Pectoral,  pertaining  to  chest  or  shoulders. 

Pelvic,  pertaining  to  the  hips. 

Fishes  are  aquatic  vertebrates,  with  either  a  cartilaginous  or 
bony  skeleton ;  they  breathe  by  means  of  gills;  are  usually  covered 
with  scales;  and  have  limbs  in  the  form  of  fins. 

External  Structure.  The  body  can  be  divided  into  three  regions, 
the  head,  trunk,  and  tail.  There  is  no  narrowing  to  mark  the 
neck,  since  the  smoother  outline  is  better  fitted  for  passing  through 
the  water.  The  general  outline  of  the  body  is  spindle  shaped, 
flattened  more  or  less  at  the  sides  to  aid  in  locomotion  by  displacing 
the  water  as  easily  as  possible. 

Scales.  The  whole  body,  except  the  head  and  fins,  is  covered 
with  scales  overlapping  toward  the  rear,  giving  protection  and  at 
the  same  time  allowing  great  freedom  of  motion.  They  are  supplied 
with  a  slimy  secretion  which  aids  in  locomotion  and  in  escape  from 
enemies.  In  some  fish,  such  as  the  trout  and  catfish,  the  scales 
are  minute  or  lacking,  but  in  any  case,  the  color  of  the  skin  corre- 
sponds to  the  fish's  surroundings  and  is  therefore  a  protection. 

Head.  The  head  is  usually  pointed,  protected  by  plates  instead 
of  scales,  and  attached  directly  to  the  trunk.  The  lack  of  a  neck 
is  no  disadvantage,  as  the  fish  can  turn  its  whole  body  as  quickly 
as  most  animals  can  turn  their  heads. 

239 


240  BIOLOGY    FOR   BEGINNERS 

The  mouth  is  usually  at  the  extreme  anterior  since  it  is  the  only 
organ  for  food-getting  or  defense,  and  it  is  provided  with  numerous 
sharp  teeth,  arranged  on  three  sets  of  jaw  bones  and  slanting  in- 
ward so  that  there  is  little  chance  for  a  victim  to  escape. 


FIG.  84.    Fish  —  External  Features. 

The  Fins  can  be  divided  into  those  on  the  median  line  and  those  which  are 
paired.  The  former  are  probably  parts  of  a  continuous  fin  which,  in  earlier 
forms,  extended  completely  around  the  body,  as  in  the  eel  or  tadpole. 

The  dorsal  fins  can  be  erected  and  are  armed  with  spines  for  protection. 
Smaller  spines  are  also  found  in  the  anal  and  pelvic  fins. 

The  caudal  fin  is  the  chief  propelling  organ  and  has  flexible  fin-rays  for  its 
support.  All  the  fins  in  the  median  line  aid  in  locomotion  and  steering. 

The  paired  fins  are  homologous  to  the  limbs  of  higher  animals.  The  pelvic 
fins  aid  in  supporting  the  fish  when  at  rest  on  the  bottom,  and  both  pairs  help 
in  balancing  and  swimming. 

The  Lateral  Line  seems  to  consist  of  a  series  of  gland-like  sacs  whose  function 
is  thought  to  be  to  provide  a  depth  or  pressure  sense. 

The  Nostrils  have  two  openings  each,  so  that  water  can  flow  through  them 
as  the  fish  swims,  bringing  with  it  the  particles  which  cause  the  sensation  of 
smell.  They  do  not  connect  with  the  throat  and  have  nothing  to  do  with 
breathing,  as  is  the  case  of  air  breathers. 

The  Scales  are  arranged  overlapping  to  the  rear,  to  give  all  possible  protec- 
tion, and  at  the  same  time  permit  perfect  freedom  of  motion,  and  offer  no 
resistance  to  the  water.  A  slippery  secretion  aids  in  locomotion  and  escape 
.'rom  enemies.  Often  their  color  is  of  advantage  in  escaping  observation,  either 
by  enemies  or  prospective  prey. 

The  Operculum  is  a  strong  covering  which  protects  the  very  delicate  gills 
from  injury.  It  has  a  slight  motion,  so  as  to  permit  the  water  to  pass  out  under- 


FISHES 


241 


neath  it.    The  free  ventral  edge  extends  far  forward  under  the  head  almost 

meeting  in  a  narrow  throat  region,  the  isthmus. 

t    All  the  above  features  are  adaptations  for  aquatic  life,  and,  together  with 

other  internal  organs,  have  made  the  typical  fish  unusually  well  suited  to  its 

environment. 

The  general  outline  of  most  fish  is  about  like  the  perch  in  having  the  flattened 
sides  and  tapering  posterior,  which  make  for  speed.  All  fish  have  the  bulk  of 
their  body  composed  of  flexible  muscle  plates  which  permit  powerful  and  free 
use  of  the  caudal  fin  in  locomotion. 


There  are  two  nasal  cavities  each  with  two  nostrils,  but  they  are 
used  for  smell  only,  since  they  do  not  connect  with  the  throat 
and  cannot  be  used  in  breathing. 

The  eyes  are  large,  somewhat  movable,  and  have  no  lids,  but 
have  a  cornea,  lens,  retina,  etc.,  somewhat  similar  to  our  own, 
and  are  entirely  different  from  the  compound  eyes  of  the  insects. 

The  ears  are  embedded  in  the  skull  and  do  not  show  externally; 
they  probably  function  as  balancing  organs  and  are  used  to  detect 
vibration,  rather  than  sound,  as  fish  have  no  sound-making  apparatus 
and  probably  cannot  "  hear  "  in  the  sense  that  we  do. 

The  Gills.  At  each  side  of  the  head  is  a  crescent-shaped  slit 
which  marks  the  rear 
border  of  the  gill  cover  or 
operculum.  These  slits 
almost  meet  on  the  ventral 
side,  leaving  only  a  narrow 
isthmus  at  the  ,  throat 
region,  and  thoroughly 
exposing  the  gills  to  the 
water.  If  we  look  inside 
the  mouth  we  can  see  that 
the  throat  has  five  slits  on 
each  side,  leaving  four 
gill  arches  between  them 

and  if  the  operculum  be  lifted  the  outer  sides  of  these  gills  can  be 
seen. 

Each  gill  consists  of  an  arch  of  bone  between  the  slits  in  the 
throat  wall,  to  which  are  attached  two  rows  of  thin- walled  thread- 


FIG.  85.     Fish  —  structure  of  gill. 


242  BIOLOGY  FOR  BEGINNERS 

like  appendages  called  the  gill  filaments.  These  filaments  are 
richly  provided  with  capillaries,  so  that  the  blood  is  brought  in 
close  contact  with  the  water  over  a  very  large  surface.  This 
permits  the  exchange  of  oxygen  (dissolved  in  water)  and  carbon 
dioxide  by  means  of  osmosis.  The  gill  arches  have  finger-like  projec- 


Courtesy  oj  the  A  merican  Museum  of  Natural  History 

FIG.  86.    Skeleton  of  European  Perch,  Percaflumatilis,  illustrat- 
ing the  bony  framework  of  the  higher  fishes.     After  Cuvier. 

The  whole  fish  is  adapted  for  thrusting  rapidly  forward  through  the  water. 
The  tapering  head  ends  in  a  sharp  prow  extending  from  the  nose  to  the  neck. 
The  brain-case  is  braced  on  all  sides  to  receive  the  forward  thrust  of  the  many- 
jointed  backbone,  which  is  driven  forward  by  the  tail.  The  fins  are  spread  upon 
bony  sticks  or  rays,  which  are  supported  by  bony  pieces  that  are  embedded 
in  the  flesh.  Between  the  supporting  pieces  and  the  fin  rays  there  are  usually 
movable  joints.  The  ventral  fins  are  fastened  beneath  the  pectoral  fins,  an 
arrangement  which  facilitates  quick  turning. 

The  propelling  muscles  and  their  bony  supports  are  extended  along  the 
sides  of  the  backbone  and  outside  the  ribs.  The  ribs  enclose  the  stomach, 
intestines  and  other  vital  organs.  These  extract  from  the  food  the  energy 
which  is  given  out  in  muscular  exertion.  The  region  of  the  gills  is  covered  by 
an  elaborate  system  of  jointed  plates. 

The  mouth  is  guarded  by  bony  jaws  which  are  attached  to  the  lower  side 
of  the  skull. 

tions  on  the  side  toward  the  throat  called  gill  rakers,  which  prevent 
food  or  dirt  from  getting  into  the  filaments  and  also  keep  the  arches 
separate  to  allow  free  circulation  of  water. 

The  water  is  taken  in  at  the  mouth,  which  is  then  closed,  forcing 
it  through  the  gill  slits  over  the  filaments  and  out  beneath  the 
operculum ;  the  forward  motion  of  the  fish  aids  in  this  process. 


FISHES  243 

Here,  as  in  all  breathing  organs,  we  find  a  large  extent  of  surface, 
thin  membranes,  and  rich  blood  supply,  all  adaptations  for  osmotic 
exchange,  together  with  protective  devices  in  the  form  of  operculum 
and  gill  rakers,  and  provision  for  a  free  circulation  of  water. 

Trunk.  Extending  along  both  sides  of  the  body  backward  from 
the  operculum  is  a  row  of  pitted  scales  with  sense  organs  beneath 
them,  known  as  the  lateral  line,  which  probably  aids  the  ears  in 
feeling  vibrations,  and  functions  as  a  pressure  organ  to  estimate 
the  depth  at  which  they  swim.  The  fins  are  the  most  characteristic 
and  noticeable  appendages  of  the  trunk  and  consist  of  a  double 
membrane,  supported  by  cartilaginous  or  spiny  rays,  and  operated 
by  powerful  muscles.  Their  shape  and  number  vary  with  the  kind 
of  fish,  but  there  are  always  two  pairs,  the  pectoral  (anterior)  and 
pelvic  (posterior)  fins,  which  are  homologous  with  the  arms  and 
legs  of  other  vertebrates.  The  other  fins  are  all  on  the  median 
(middle)  line  of  the  trunk,  there  being  sometimes  two  dorsal  fins; 
always  a  large  tail  (caudal)  fin,  and  an  anal  fin  just  back  of  the 
vent.  In  general  the  fins  are  beautifully  fitted  for  locomotion 
in  the  water,  but  they  are  differently  used  in  this  process,  the  caudal 
fin  being  the  chief  propelling  and  steering  organ.  The  paired 
fins  aid  in  locomotion  and  in  balancing,  and  also  support  the  body 
when  resting  on  the  bottom.  The  other  median  fins  aid  in  steering 
and  are  often  provided  with  sharp  spines  for  defense  as  well. 

The  bulk  of  the  fish's  body  consists  of  powerful  muscles.  The 
flexible  backbone  is  made  up  of  very  numerous  vertebrae,  which, 
together,  permit  the  fins  to  be  utilized  to  the  fullest  extent  and 
provide  a  system  of  aquatic  locomotion,  second  to  none  in  the 
world,  aided  as  it  is  by  the  pointed,  scale-covered,  slippery 
body. 

Internal  Structure.  Digestive  System.  The  food  of  most  fishes 
consists  of  other  aquatic  animals,  though  a  few  are  vegetarians. 
It  is  grasped  by  the  mouth,  but  the  teeth  serve  only  for  prehension 
and  not  for  chewing.  On  this  account  the  gullet  is  large  and  short, 
the  stomach  provided  with  powerful  digestive  fluids  and  usually 
with  finger-like  outgrowths  (caeca)  to  increase  the  digestive  surface. 
As  in  most  carnivorous  animals,  the  intestine  is  rather  short, 


244 


BIOLOGY   FOR  BEGINNERS 


making  only  two  loops,  and  opening  into  it  is  the  duct  from  a  well- 
developed  liver  between  whose  lobes  the  gall  sac  can  be  found. 

Circulation.  The  fish  has  a  heart  consisting  of  two  chambers, 
an  auricle  and  a  ventricle,  located  just  posterior  to  the  isthmus. 
So  it  is  literally  true  that  its  "  heart  is  in  its  throat."  The  blood 
leaves  the  heart  by  a  large  artery  that  branches  to  each  of  the 
gills,  in  whose  filaments  it  is  relieved  of  its  carbon  dioxide.  Then 
laden  with  oxygen  it  flows  into  a  dorsal  artery  with  branches  to 

all  the  muscles  and  in- 

'""""""•  *••"-"•  ternal   organs  where   it 

exchanges  this  oxygen 
for  carbon  dioxide.  The 
blood  which  flows  to  the 
digestive  organs  receives 
the  digested  food-stuffs 
which  they  have  pre- 
pared, and  passes 
through  the  liver  and 
so  back  to  the  auricle  of 
the  heart.  Thus  it  hap- 
pens that  the  heart  is  always  pumping  blood  that  is  rich  in  nutrients 
and  carbon  dioxide  but  poor  in  oxygen.  The  course  of  the  blood 
stream  is  from  the  ventricle  of  the  heart,  to  gills,  to  general  circu- 
lation and  digestive  organs,  to  liver,  and  back  to  auricle  of  the 
heart  again,  though  a  part  passes  through  the  kidneys  each  time, 
where  urea  and  other  wastes  are  removed. 

Nervous  System.  The  central  nervous  system  in  all  vertebrates 
is  located  in  the  dorsal  body  cavity,  protected  by  outgrowths  from 
the  spinal  column.  This  arrangement  is  entirely  different  from 
that  found  in  the  invertebrates,  where  the  nervous  system  lies 
along  the  ventral  side  and  is  not  separated  from  the  other  internal 
organs. 

In  the  case  of  most  fishes  the  nervous  system  consists  of  the 
spinal  cord,  extending  the  whole  length  of  the  body,  protected  by 
arches  of  bone  attached  to  each  vertebra.  From  it  many  nerves 
extend  to  the  muscles  and  internal  organs.  At  the  anterior,  the 


FIG.  87.     Diagram  of  circulation  in  fish. 


FISHES  245 

cord  enlarges  to  form  a  brain,  entirely  different  in  structure  from 
the  so-called  brains  of  the  lower  forms,  in  that  it  has  developed 
separate  regions  for  different  functions.  The  fish's  brain  consists 
of  five  principal  parts.  Beginning  at  the  anterior,  come  the  olfactory 
lobes  from  which  the  nerves  of  smell  extend  to  the  nostrils.  Pos- 
terior to  these,  and  considerably  larger,  are  the  two  lobes  of  the 
cerebrum,  which  control  the  voluntary  muscles  of  the  animal. 
The  largest  parts  of  the  brain  are  the  two  optic  lobes  connected 
directly  with  the  eyes  and  concerned,  of  course,  with  the  sense  of 
sight.  Behind  them  comes  the  cerebellum,  and  finally  the  enlarged 
end  of  the  spinal  cord,  the  medulla,  both  of  which  have  to  do  with 
regulating  muscular  action  and  the  work  of  the  internal  organs.  The 
medulla  is  also  a  region  from  which  branch  many  important  nerves. 

The  brain  as  a  whole,  compared  with  other  vertebrates,  is  not 
highly  developed.  The  cerebrum,  the  center  of  voluntary  control, 
is  actually  smaller  than  the  optic  lobes,  and  the  whole  brain  does 
not  fill  the  cranium  or  skull  cavity,  which  is  partly  occupied  by  a 
protective  liquid.  It  is  only  when  compared  with  the  invertebrate 
forms,  that  the  real  advance  of  the  fish  brain  can  be  realized.  In 
them  there  were  no  special  parts  for  separate  uses,  no  division  of 
labor  or  specialization,  and  so  a  highly  developed  instinct  was  the 
best  such  a  brain  could  achieve. 

In  the  vertebrate,  the  development  of  specialized  parts  of  the 
brain,  though  very  primitive  at  first,  paved  the  way  for  a  cerebrum 
which  would  exceed  all  the  other  brain  regions  in  bulk,  and  control, 
not  only  voluntary  motion,  but  thought  and  reason,  as  well.  So 
when  studying  the  simple  brain  of  the  fish,  do  not  forget  that  it 
contains  the  possibilities  of  great  advance,  and  is  to  be  the  line 
along  which  the  highest  vertebrate  development  will  be  attained. 

Air  Bladder.  Another  organ,  simple  in  the  fish,  but  which  has 
a  great  future  before  it,  is  the  air  bladder  which  is  found  in  most 
species.  This  consists  of  a  thin-walled  elliptical  sac,  located  in 
the  dorsal  part  of  the  visceral  cavity  and  sometimes  connected 
with  the  throat  by  a  tube.  Its  function  is  to  assist  the  fish  in 
maintaining  a  level  in  the  water;  by  contraction  of  its  walls  the 
fish  can  sink,  and  by  expansion,  rise  without  other  effort. 


246 


BIOLOGY   FOR   BEGINNERS 


It  develops  in  the  embryo  fish  as  an  outgrowth  from  the  throat, 
extending  back  and  enlarging  into  the  present  form,  and  often 
losing  all  connection  with  the  outer  air.  It  is  in  precisely  similar 
manner  that  the  lungs  of  all  higher  forms  push  out  from  the  throat, 
while  retaining  their  connection  with  the  mouth  and  performing 
an  entirely  different  function.  Yet  they  are  regarded  as  of  like 
origin  and  structure,  so  the  lungs  are  homologous  to  the  air  bladder 
of  fishes,  but  by  no  means  analogous  (or  like  in  function). 

In  this  connection  it  is  interesting  to  note  that  in  certain  Aus- 


F  6  H 

FIG.  88.     Embryonic  development  of  fish. 

A,  unfertilized  egg;  gd,  germinal  disc;  y,  yolk;  B,  zygote  formed  by  union 
of  ovum  and  spermatozoon;  C,  D,  cleavage;  E,  young  embryo  showing  neural 
groove  at  left;  F,  showing  yolk  nearly  overgrown  by  the  vascular  membrane 
(blastoderm)  growing  out  from  embryo;  G,  embryo  with  "yolk  sac";  H,  young 
fish,  just  hatched,  with  yolk  sac  not  yet  absorbed.  From  Pearse. 


tralian  fishes  the  air  bladder  is  actually  used  as  a  lung  and  the  gills 
are  poorly  developed  for  breathing. 

As  the  development  of  higher  forms  goes  on,  the  simple  air 
bladder  becomes  two  lobed,  its  walls  develop  ridges,  and  finally 
many-celled  chambers  which  enormously  increase  the  ulterior 
surface.  To  the  walls  of  these  delicate  cells  a  network  of  capillaries 
brings  the  blood,  and  devices  are  provided  to  pump  air  in  and  out. 
Thus  from  the  air  bladder  of  the  fish,  the  lung  of  a  bird  or  man 
may  trace  its  origin. 


FISHES 


247 


Life  History.  The  breeding  habits  of  fish  vary  so  greatly  that 
it  is  difficult  to  make  any  general  statements  about  their  life  history 
to  which  there  will  not  be  many  exceptions. 

The  eggs  vary  in  size  from  over  an  inch  in  skate,  to  the  micro- 
scopic offspring  of  the  herring.  Their  number  may  vary  from  five 
hundred  in  the  trout  to  millions  in  cod,  sturgeon,  or  flounder. 
The  eggs  are  fertilized  after  being  laid,  by  means  of  the  spermatic 
liquid  (milt)  which  the  male  sprays  over  them,  sometimes  stirring 
the  eggs  and  milt  together  so  that  more  shall  be  fertilized.  There 
is  little  chance  that  all  the  eggs  will  be  fertilized,  since,  as  in  the 


Stickleback  Dogfish 

FIG.  89.     Fish  nests.  From  Pearse. 

plant,  a  sperm  cell  must  reach  each  egg  cell  if  it  is  to  develop. 
Hence  the  large  number  of  eggs  is  partly  to  make  up  for  the  small 
chance  of  fertilization.  The  eggs  and  young  are  prey  to  many 
other  fish  and  similar  enemies,  while  man  destroys  the  adults  for 
food,  fertilizer,  and  fun.  Out  of  enormous  numbers  of  eggs,  so 
few  survive,  in  some  cases,  that  artificial  fish  culture  has  to  be 
utilized  to  prevent  total  destruction  of  certain  species.  In  many 
cases  both  the  fertilization  and  the  care  of  young  are  left  to  chance, 
while  in  others,  such  as  the  bass,  sunfish,  trout,  and  catfish,  a  sort 
of  nest  is  made  on  the  stream  bottom,  where  the  eggs  are  guarded 
by  the  male,  or  may  be  covered  with  sand  for  protection. 


248  BIOLOGY  FOR  BEGINNERS 

As  development  proceeds  the  form  of  the  embryo  fish  may  be 
seen  within  the  egg  from  which  it  soon  emerges,  retaining  the  yolk 
of  the  egg  attached  to  the  body,  to  be  absorbed  as  nourishment 
until  the  tiny  fish  can  shift  for  itself,  and  grow  gradually  to  its 
normal  size. 

Life  History  of  the  Salmon.  While  no  one  fish  can  be  taken  as  a 
type  of  all,  the  life  history  of  the  Pacific  salmon  is  as  well  known 
as  any  and  since  it  is  so  familiar  an  article  of  food,  we  shall  take  up 
its  breeding  habits  somewhat  in  detail. 

The  adult  salmon  lives  in  the  ocean  all  along  the  northern 
Pacific  coasts.  In  spring  or  early  summer  both  sexes  migrate  in 
enormous  numbers  up  the  Columbia  and  other  rivers  often  to  a 
distance  of  one  thousand  miles.  It  is  during  these  "  runs  "  that 
the  canners  make  their  annual  catches  by  means  of  barriers  or 
machines  which  scoop  up  the  passing  fish. 

This  migration  may  be  for  the  purpose  of  finding  greater  safety, 
cooler  water,  or  better  food,  or  it  may  be  a  relic  of  the  time  when 
they  may  have  been  entirely  fresh-water  fish.  At  all  events  they 
begin  in  March  to  make  their  last  journey.  Slowly  at  first  and 
later  many  miles  per  day  they  work  their  way  against  the  current 
to  the  spawning  beds  far  from  the  sea. 

Here,  in  water  not  warmer  than  54  degrees,  each  female  deposits 
about  3500  eggs.  The  male  spreads  over  them  the  "  milt  "  or 
spermatic  fluid  at  large  in  the  water.  It  is  much  like  wind  pollena- 
tion  in  flowers  and  many  eggs  are  not  reached  by  the  sperms, 
hence  do  not  develop. 

The  males  are  brilliantly  colored  at  the  breeding  season  but 
both  sexes  soon  lose  their  beauty  and  strength,  partly  in  fighting 
other  fish  and  partly  by  injuries  from  the  stones  in  the  spawning 
beds. 

The  eggs  are  deposited  on  fine  gravel  and  the  process  extends 
over  several  days  after  which  the  strength  of  the  parents  seems 
to  be  exhausted  and  both  die. 

After  from  thirty  to  forty  days  the  eggs  hatch,  but  as  usual  with 
fish,  the  yolk  remains  attached  until  all  is  absorbed  in  growth  and 
the  fry,  as  they  are  called,  can  shift  for  themselves. 


FISHES  249 

Although  many  young  salmon  fall  prey  to  other  fish  the  majority 
find  their  way  back  to  the  ocean  where  they  reach  adult  life,  and, 
if  they  escape  the  canner's  machines,  live  to  repeat  the  self-sacrifice 
of  their  parents. 

Adaptations.  The  study  of  the  fish  reveals  an  animal,  first  of 
all  adapted  for  aquatic  life,  and  nearly  all  features  of  its  structure 
and  habits  tend  to  this  result,  as  the  following  summary  will  show. 


SUMMARY  OF  ADAPTATIONS 

For  Locomotion  in  Water. 

1.  Shape  of  body,  slimy  secretion. 

2.  Scales,  fins. 

3.  Flexible  spinal  column  and  powerful  muscles. 

For  Life  in  Water  (see  above,  also). 

1.  Gills  for  respiration. 

2.  Air  bladder,  to  regulate  depth. 

3.  Lateral  line  to  determine  pressure. 

4.  Structure  of  eye,  spherical  lens. 

For  Protection. 

1.  Color,  dark  above,  light  below. 

2.  Scales,  spines,  teeth. 

3.  Speed,  to  escape  enemies. 

For  Food  Getting. 

1.  Location  and  size  of  mouth. 

2.  Shape  and  location  of  teeth. 

3.  Wide  gullet  and  powerful  digestion. 

4.  Speed. 

COLLATERAL   READING 

General  description  and  structure:  American  Food  and  Game  Fishes, 
Jordan,  pp.  364-367;  Fishes,  Chap.  XXXIII,  Jordan,  p.  508;  Fishes, 
Chap.  X  (adaptations),  Jordan,  pp.  51-78;  Familiar  Fish,  McCarthy, 
Chap.  7;  American  Natural  History,  Hornaday,  pp.  380-387;  Life  in 
Ponds  and  Streams,  Furneaux,  p.  353;  General  Zoology,  Linville  and 


250  BIOLOGY  FOR  BEGINNERS 

Kelley,  p.  305;  Elementary  Zoology,  Packard,  pp.  142-175;  Animal 
Structures,  French,  pp.  169-178;  Winners  in  Life's  Race,  Buckley,  pp. 
20-42;  Economic  Zoology,  Osborne,  pp.  338-355;  Elementary  Lessons  in 
Zoology,  Needham,  pp.  161-378;  Practical  Zoology,  Davidson,  pp.  185- 
199;  Comparative  Zoology,  Kingsley,  pp.  21-39;  Elementary  Zoology, 
Galloway,  pp.  281-295;  Elements  of  Biology,  Hunter,  pp.  271-278;  Ap- 
plied Biology,  Bigelow,  pp.  419-424;  Elementary  Biology,  Peabody  and 
Hunt,  pp.  120-137;  Forms  of  Animal  Life,  Rolleston,  pp.  83-102. 

Advanced  works  on  structure:  Advanced  Zoology,  Packard,  pp.  411-460; 
Textbook  of  Zoology,  Claus  and  Sedgwick,  pp.  120-150;  Forms  of  Animal 
Life,  Rolleston,  pp.  83-98;  Anatomy  of  the  Vertebrates,  Huxley,  pp.  59-65. 

Classification  and  kinds  of  fish:  American  Food  and  Game  Fish,  Jordan 
(key),  pp.  29-34;  Elements  of  Zoology,  Davenport,  pp.  298-324;  Fresh 
Water  Aquarium,  Eggeling,  pp.  107-216;  Pet  Book,  Comstock,  pp.  226-245; 
Handbook  of  Natural  History,  Comstock,  pp.  149-180;  Nature  Study 
Leaflets  (bound),  Cornell,  pp.  157-166;  Winners  in  Life's  Race,  Buckley, 
pp.  43-69. 

Economic  Value  and  Life  History:  Fishes  (life  history),  Jordan,  pp.  1-24; 
Fishes  (as  food),  Jordan,  pp.  129-148;  Familiar  Fish  (propagation),  Mc- 
Carthy, Chap.  2;  American  Natural  History,  Hornaday,  pp.  375-377; 
Practical  Biology,  Smallwood,  pp.  103-112;  U.  S.  Fish  Commission  Report, 
1897;  Economic  Zoology  (good),  Kellogg  and  Doane,  Chap.  21;  Elementary 
Biology,  Peabody  and  Hunt,  pp.  137-150;  Talks  About  Animals,  pp.  7-35; 
Animal  Life,  Thompson,  pp.  109-110,  253-256. 


SUMMARY 

Characteristics:  bony  skeleton,  gills,  scales,  fins. 
External  Structure. 

Shape,  spindle  outline  for  easy  swimming. 

Scales,  for  protection  and  ease  of  motion  (cf.  crayfish). 

Head. 

Mouth  and  teeth  for  prehension  and  defence. 

Nasal  cavities  for  smell,  not  breathing. 

Eyes,  with  lens,  cornea,  etc.,  but  no  lids  (cf.  crayfish). 

Ears,  internal,  detect  vibration  or  balance. 
Gills. 

Gill  openings,  two  at  sides  of  head. 

Operculum,  cover  over  gills. 

Gill  arches,  four,  bony,  hook  shaped,  support  the 

Filaments,  numerous,  much  surface,  thin,  capillaries. 

Gill  rakers,  clean  and  spread  arches. 
Trunk. 

Lateral  line,  for  depth  sense. 

Fins,  a  double  membrane  supported  by  rays. 

Paired,  pelvic,  posterior,  for  locomotion  and  balance, 
pectoral,  anterior,  for  locomotion  and  balance. 


FISHES  251 


Median,  caudal,  locomotion,  and  steering  (tail), 
dorsal  (back)  steering, 
anal  (vent)  steering. 
Body  very  muscular. 
Internal  Structure. 
Digestive  system. 

Teeth  for  prehension,  not  chewing. 
Stomach,  with  caeca,  powerful  fluids. 
Intestine  short  and  large,  liver  large. 
Circulation. 

Heart  two  chambered,  anterior,  ventral. 
Blood  flows  to  gills,  to  body,  to  heart,  to  gills,  etc. 
Nervous  system. 

Brain,  separate  parts  for  different  functions  (result), 
Spinal  cord,  dorsal,  protected  by  vertebrae. 
Air  Bladder. 

Outgrowth  from  throat. 
Function:  to  regulate  depth. 
Homologue  of  lung. 
Life  history. 

Eggs  small  and  numerous.     (Why?) 
Externally  fertilized. 
Slight  parental  care,  many  enemies. 
Embryo  retains  yolk  sac  for  food. 

Grows  gradually,  not  by  stages.     (Why?) 
Life  history  of  the  salmon. 
Adaptations. 

See  summary  in  text. 


CHAPTER  XXVHI 

THE  AMPHIBIA 
THE   FROG   AND   ITS   RELATIVES 

Vocabulary 

Transition,  period  of  change. 
Vegetarian,  using  vegetable  food. 
Carnivorous,  using  animal  food. 
Constitute,  to  make  up  or  compose. 
Pulmonary,  pertaining  to  the  lungs. 
Aerated,  supplied  with  air. 
Viscera,  all  the  internal  body  organs. 

Particular  interest  attaches  to  this  group  because  of  the  fact 
that,  in  their  life  history,  we  can  see  the  steps  in  development 
between  the  fishlike  animals  adapted  solely  for  aquatic  life  and 
the  land  animals  which  cannot  live  under  water. 

In  this  transition  from  water  to  land  forms,  many  strange 
combinations  of  gills  and  lungs,  fins  and  legs,  have  occurred, 
gills  being  found  on  animals  with  legs,  and  fins  sometimes  ac- 
companied by  lungs.  All  together  this  is  a  very  good  object 
lesson  in  the  development  and  adaptations  of  animal  forms. 

The  name  amphibia,  meaning  "  having  two  lives,"  refers  to 
the  fact,  that  they  usually  are  aquatic,  fishlike  animals  when 
young,  and  abandon  that  manner  of  life  for  the  land  when  they 
become  adults.  This  series  of  changes  is  called  a  metamorphosis, 
just  as  was  the  life  history  of  some  insects. 

Characteristics.  The  characteristics  of  the  group  may  be 
summarized  as  follows,  though  there  are  some  exceptions: 

1.  They  undergo  a  metamorphosis. 

2.  Eggs  are  directly  fertilized  as  laid. 

3.  Usually  they  are  covered  by  a  smooth  skin. 

252 


THE   FROG  AND   ITS  RELATIVES 


253 


254  BIOLOGY    FOR   BEGINNERS 

4.  Larval  forms  are  vegetarian;  adults,  carnivorous. 

5.  The  heart  is  three  chambered,  and  circulation  well  developed. 

6.  The  brain,  especially  the  cerebrum,  better  developed  than  in 

fish. 

Among  the  representatives  of  this  curious  group,  are  several 
common  animals.  Frogs,  toads,  tree-toads,'  newts  and  salamanders 
are  all  familiar  both  by  sight  and  sound. 

The  Frog.  The  frog  will  be  taken  as  a  type  not  only  because 
common  and  convenient,  but  also  because  of  the  resemblance  of  its 
structure  to  that  of  the  human  being. 

In  the  work  with  the  frog,  it  is  particularly  desirable  to  compare 
its  structure  and  development  with  that  of  the  fish,  whenever 
possible,  noting  those  points  in  which  it  is  more  highly  developed 
and  the  differences  which  its  land  life  has  made  necessary  in  its 
structure. 

External  Features.  The  frog's  body  is  short,  broad,  and  angular, 
evidently  not  as  well  adapted  for  submarine  locomotion  as  the 
fish,  nor  has  it  achieved  the  graceful  form  of  a  highly  specialized 
land  animal.  The  covering  is  a  loose  skin,  colored  to  resemble  its 
surroundings,  and  provided  with  no  scales  nor  hairs,  but  supplied 
beneath  with  many  blood  capillaries.  It  is  evident  that  the  skin 
is  not  for  defense  like  the  scaly  armor  of  the  fish  but  attains  some- 
what the  same  end  by  its  protective  coloration.  Its  thinness  and 
rich  blood  supply  permit  a  certain  amount  of  respiration  to  take 
place  through  it.  Many  amphibians  absorb  water  through  the 
skin  instead  of  by  drinking.  Some  secrete  a  slimy  mucus  which 
assists  in  locomotion  and  escape  from  enemies.  The  head  is  broad, 
flat,  and  attached  directly  to  the  body.  The  nostrils  are  located 
near  the  anterior  and  connect  directly  with  the  mouth  cavity, 
thus  permitting  them  to  be  used  for  respiration.  They  can  be 
closed  by  a  valve-like  flap  when  under  water. 

Head  Structures.  The  Mouth.  The  mouth  is  enormous  and 
extends  literally  from  ear  to  ear.  This  is  a  very  necessary  adapta- 
tion for  food-getting  as  the  insects  which  constitute  its  principal 
diet  have  to  be  snapped  up  in  this  veritable  trap.  Another  strik- 
ing adaptation  for  the  same  purpose  is  the  arrangement  of  the 


THE   FROG   AND   ITS   RELATIVES 


255 


tongue.  This  is  attached  at  the  front  of  the  lower  jaw,  is  very 
muscular,  and  has  two  sticky  fingerlike  projections  at  its  tip. 
This  peculiar  tongue  can  be  flipped  out  of  the  mouth  so  quickly 

FftOG 


ffjorecnrf    Pos/no* 

IM      WAT  fit 


FIG.  91.     Frog.     External  Features. 

Fig.  i.  Mouth  Structure.  —  The  mouth  is  shown  as  if  opened  quite  flat. 
There  are  no  teeth  on  the  lower  jaw,  as  they  would  interfere  with  the  tongue 
when  extended  as  in  Fig.  2.  The  teeth  on  the  roof  of  the  mouth  are  just  where 
they  will  catch  any  insect  which  has  been  flipped  into  the  mouth  by  the  tips 
of  the  tongue. 

The  openings  into  the  vocal  sacs  enable  the  frog  to  inflate  his  throat  and, 
with  these  hollows  as  a  sounding  board,  make  such  loud  calls  in  the  mating 
season. 

Notice  that  the  food  has  to  pass  over  the  trachea  to  reach  the  gullet,  so  the 
former  is  protected  by  a  sort  of  lip-like  valve. 

The  curved  enlargements  by  the  eustachian  tubes  are  caused  by  the  down- 
ward projection  of  the  eyeballs. 

Figs.  2,  3,  and  4,  show  stages  in  the  operation  of  the  frog's  tongue,  in  catch- 
ing insects. 

The  tip  is  two  lobed  and  sticky,  the  mouth  enormous  in  width,  and  the 


256  BIOLOGY    FOR   BEGINNERS 

speed  of  the  tongue  is  so  great  as  almost  to  elude  the  sight,  so  it  all  makes 
a  very  efficient  food  getting  device. 

Usually  the  frog  jumps  at  the  same  time  it  extends  its  tongue,  thus  increas- 
ing its  range  very  greatly. 

Toads  also  have  the  same  adaptation,  and  some  salamanders  are  even  better 
provided. 

Fig.  5  shows  the  position  of  rest  in  the  water,  with  the  prominent  eyes  and 
anteriorly  placed  nostrils,  just  above  the  surface.  In  this  position,  either  at 
rest  on  the  bottom,  or  afloat  with  hind  legs  extended,  the  frog  is  almost  invisible 
and  thus  escapes  its  enemies. 

Note  the  inturned  front  feet,  mere  props  and  the  hind  legs,  folded  ready  to 
swim  or  leap  on  the  instant. 

that  the  eye  cannot  see  the  motion;  the  insect  sticks  to  it  and  is 
instantly  thrown  back  within  the  capacious  jaws,  just  where  a 
set  of  teeth  on  the  roof  of  the  mouth  will  hold  and  crush  it.  There 
are  no  teeth  on  the  lower  jaw,  as  they  would  interfere  when  the 
tongue  was  thrown  out  over  them.  Those  on  the  upper  jaw  are 
small,  and  in  toads  both  sets  are  lacking  entirely,  as  the  real  organ 
of  prehension  in  either  case  is  the  remarkable  tongue. 

As  we  look  inside  the  frog's  mouth  the  nostril  openings  can  be 
seen  near  the  anterior  of  the  upper  jaw;  the  tongue  folded  back 
occupies  the  floor  of  the  lower  jaw;  farther  back  at  the  sides  are 
the  openings  of  the  eustachian  tubes  from  the  ears;  and  at  the 
extreme  rear,  in  the  middle,  can  be  found  the  wide  gullet  and  slit- 
like  opening  of  the  breathing  tube  or  trachea.  The  walls  of  the 
throat  are  loose  and  can  be  greatly  expanded  with  air  when  the 
frog  is  calling,  thus  acting  as  resonating  chambers.  This  gives 
great  volume  to  the  sound  for  which  all  frogs  are  noted. 

Other  Organs.  The  eye  of  the  frog  is  one  of  the  most  beautiful 
in  all  the  animal  kingdom,  having  the  black  pupil  surrounded  by  a 
handsome  bronze  colored  iris  of  large  size.  It  projects  conspicuously 
from  the  top  of  the  head,  but  can  be  withdrawn,  level  with  the 
skull.  It  is  protected  by  lids  and  an  extra  covering,  the  nictitating 
membrane,  which  can  be  raised  from  below  and  probably  protects 
the  eye  when  under  water. 

The  location  of  the  nostrils  at  the  very  tip  of  the  head,  and  the 
high  projection  of  the  eyes  enable  the  frog  both  to  see  and  breathe 
while  the  rest  of  the  body  is  covered  by  water.  When  in  this 


THE   FROG   AND   ITS  RELATIVES  257 

position  it  is  able  to  avoid  observation,  and  so  escapes  from  large 
water  birds  which  feed  upon  them. 

The  ears  are  located  just  behind  the  eyes  and  consist,  externally, 
of  the  round  tympanic  membrane,  which  is  connected  with  the 
internal  ear  beneath  and  also  with  the  mouth  cavity,  by  means  of 
the  eustachian  tube. 

Legs.  The  anterior  legs  are  short  and  weak.  They  are  provided 
with  four  inturned  toes,  which  help  little  in  locomotion  but  serve 
as  supports  to  the  body  when  on  land.  The  hind  legs,  however, 
are  enormously  developed  and  adapted  in  several  ways  for  leaping 
and  swimming.  The  thigh  and  calf  muscles  are  very  powerful 
and  are  so  attached  to  the  hips  that  they  move  the  legs  as  very 
efficient  levers,  in  locomotion.  Added  to  this  is  the  great  develop- 
ment of  the  ankle  region  and  toes,  which  together  are  longer  than 
the  lower  leg  and  add  greatly  to  the  leverage  of  these  organs.  Be- 
tween the  five  long  toes  is  developed  a  broad  flexible  web  membrane, 
which  accounts  for  the  frog's  notable  ability  as  a  swimmer. 

Some  frogs  can  leap  fifty  times  their  own  length  or  twenty  times 
their  height,  while  a  man,  to  equal  this  feat  would  have  to  make  a 
broad  jump  of  three  hundred  feet  or  clear  the  bar  at  a  height  of 
one  hundred  and  twenty  feet. 

The  legs  of  the  frog  are  homologous  to  the  paired  fins  of  the 
fish  but  resemble  much  more  closely  our  own  arms  and  legs.  A 
study  of  a  prepared  skeleton  of  the  frog  shows  that  the  foreleg 
has  the  same  regions  as  our  arm.  The  hind  leg  even  more  closely 
resembles  our  leg,  though  with  many  differences  due  to  being 
adapted  for  very  different  functions.  Still  the  homology  is  plain 
as  the  following  table  shows. 


258  BIOLOGY   FOR  BEGINNERS 

COMPARISON  OF  APPENDAGES  OF  FROG  AND  MAN 


Front  leg  and  arm 

Frog 

Man 

Upper  arm  (humerus) 
Lower  arm  (radius  and  ulna) 
Wrist  (carpus) 
Hand  (metacarpus) 
Fingers  (phalanges) 

Short  and  weak 
Short,  bones  united 
Very  short,  stiff 
Turned  inward 
Four,  short  and  weak 

Long  and  muscular 
Long,  bones  separate 
Longer  and  flexible 
Straight 
Five,  long  and  flexible 

Hind  leg  and  leg 

Upper  leg  (femur) 

Lower  leg  (tibia  and  fibula) 

Ankle  (tarsus) 
Foot  and  toes  (metatarsus 
and  phalanges) 

Very  long  and  muscular 

Very  long,  bones  united 

Very  greatly  lengthened 
Five,  very  long  webbed 
toes 

Medium  length,  not  so 
muscular  in  propor- 
tion 
Medium  length,  bones 
separate 
Short 
Five   short    toes,    not 
webbed 

Not  only  are  the  regions  and  the  bones  similar  in  general  structure, 
but  many  of  the  muscles,  blood  vessels,  and  nerves  of  the  limbs  of 
man  and  frog  are  of  similar  form  and  name.  The  chief  difference 
lies  in  the  fact  that  man  has  developed  his  forelegs  into  organs  for 
prehension  (grasping)  and  no  longer  uses  them  in  locomotion. 
This  has  resulted  in  his  erect  position  and  has  produced  many 
changes  in  structure  to  adapt  the  arm  and  hand  for  its  altered 
function. 

The  muscles  of  the  fish  are  in  the  form  of  flat  plates,  extending 
across  the  body  and  moving  it  as  a  whole,  while  in  the  frog,  the 
muscle  tissue  is  grouped  into  true  "  muscles  "  like  our  own,  at- 
tached to  bones  by  tendons,  and  acting  on  them  as  levers,  thus 
marking  a  great  advance  in  structure,  and  permitting  greater 
variety  of  motions. 

The  Digestive  System.  The  digestive  system  of  any  animal 
begins  with  the  mouth,  teeth,  and  food -getting  adaptations  which 
we  have  already  described  in  this  case. 


THE  FROG  AND  ITS  RELATIVES  259 

A  short  gullet  connects  the  large  mouth  cavity  with  the  stomach 
which  is  an  oval  enlargement  of  the  digestive  tube,  set  diagonally 
in  the  body  cavity  and  partly  covered  by  the  liver  which  is  anterior 
and  ventral  to  it.  Continuing  from  the  stomach  is  the  intestine, 
of  medium  length,  coiled,  and  enlarging  near  the  vent  into  a  short, 
broad  rectum  and  cloaca.  The  digestive  tract  is  longer  than  that 
of  the  fish,  but  the  fingerlike  projections  (caeca)  are  lacking  in 
the  stomach,  the  absorbing  surface  being  increased  by  the  coiled 
intestine,  instead.  Connected  with  the  food  tube  are  the  usual 
digestive  glands,  the  salivary  and  mucous  glands  in  mouth  and 
gullet,  gastric  glands  in  the  walls  of  the  stomach,  and  the  large 
liver  and  smaller  pancreas  opening  into  the  intestines. 

Here  as  usual  we  have  the  essential  features  of  any  vertebrate 
digestive  system:  a  tubular  canal,  provided  with  large  extent  of 
surface  for  absorption  by  osmosis,  and  a  series  of  glands  which 
secrete  the  fluids  used  to  get  the  food  into  soluble  form  for  this 
absorption. 

Circulatory  System.  In  so  complicated  an  animal  as  the  frog, 
it  would  be  expected  that  the  circulatory  system  would  need  to  be 
better  developed  than  in  the  fish,  especially  as  the  lungs  are  present 
for  the  first  time,  to  purify  the  blood.  To  provide  for  this  added 
burden,  we  find  a  three-chambered  heart  located  well  forward 
in  the  body  cavity,  and  consisting  of  two  auricles  and  one  muscular 
ventricle.  Extending  from  the  ventricle  is  a  large  artery  which 
at  once  divides  in  two  branches  like  a  letter  Y  and  each  of  the  arms 
again  divides  into  three  separate  arteries  on  each  side.  The 
anterior  pair  of  these  branches  (the  carotids)  carries  blood  to  the 
head;  the  middle  pair  arch  around  to  the  back  of  the  body  cavity 
and  unite  to  form  the  dorsal  aorta  which  supplies  the  muscles 
and  viscera;  while  the  posterior  (pulmonary)  arteries  carry  the 
blood  to  the  lungs  and  skin  for  purification. 

The  blood  supplied  to  the  muscles  returns  laden  with  carbon 
dioxide  and  other  oxidation  products,  while  that  going  to  the  di- 
gestive tract  takes  up  the  digested  foods  as  well.  It  returns  by 
way  of  the  veins,  in  part  to  the  liver,  and,  finally,  all  to  the  right 
auricle  of  the  heart.  Meanwhile  the  blood  which  went  to  the 


260  BIOLOGY   FOR  BEGINNERS 

lungs  and  skin  has  been  relieved  of  its  carbon  dioxide  and  re- 
supplied  with  oxygen,  and  this  returns  by  the  pulmonary  veins 
to  the  left  auricle  of  the  heart.  The  blood  from  both  the  general 
and  the  pulmonary  circulation  then  enters  the  ventricle,  but  by 
means  of  a  complicated  valve,  that  having  most  oxygen  is  sent  to 
the  head  and  brain.  The  next  best  goes  out  into  the  aorta,  while 
that  with  most  carbon  dioxide  is  diverted  into  the  pulmonary 
arteries  and  goes  to  the  lungs  and  skin. 

On  each  complete  trip,  some  of  the  blood  passes  through  the 
kidneys,  so  that  all  of  the  nitrogenous  waste  can  be  removed  as 
urine.  Really  the  purest  blood  in  an  animal's  body  is  that  which 
has  just  left  these  very  important  organs,  even  though  it  may 
have  more  carbon  dioxide  than  when  leaving  the  lungs. 

The  blood  which  returns  from  the  digestive  tract  is  gathered 
into  a  large  vein  (portal)  and  passes  through  the  liver,  where 
some  food  substances  may  be  stored,  and  certain  impurities  re- 
moved, after  which  it  flows  back  to  the  right  auricle. 

Several  important  differences  will  be  noted  in  the  frog's  circula- 
tory system,  as  compared  with  the  fish.  The  frog's  heart  is  three 
chambered  and  is  located  farther  back  in  the  body;  the  blood 
leaves  the  heart  in  two  circuits,  the  pulmonary  and  the  general, 
while  in  the  fish,  it  makes  only  one  continuous  trip.  In  other 
words,  the  blood  twice  returns  to  the  heart  of  the  frog  in  any  single 
complete  circulation,  and  only  once  in  the  fish. 

Respiration.  In  the  larval  form,  as  a  tadpole,  the  young  frog 
breathes  by  means  of  gills  but  the  adult  develops  a  pair  of  simple 
lungs,  opening  into  the  throat  by  a  trachea  and  glottis.  These 
lungs  are  rather  cone-shaped,  sac-like  organs,  whose  inner  walls 
are  honey-combed  with  delicate  air  cells  provided  with  many  blood 
capillaries  so  that  the  conditions  for  osmosis  are  fulfilled. 

The  frog  has  no  ribs  or  diaphragm  to  expand  the  lungs  so  that 
air  may  come  in,  and  is  therefore  forced  to  "  swallow  "  whatever 
air  it  gets  by  a  sort  of  pumping  motion  of  the  throat  which  can  be 
observed  in  any  living  frog.  Air  is  taken  in  through  the  nostrils, 
which  are  then  closed  and  the  air  "  swallowed  "  by  the  action  of 
the  abdominal  muscles.  The  elasticity  of  the  lung  tissue  forces 


THE  FROG  AND  ITS  RELATIVES 


261 


the  air  out  again.    The  slight  throbbing  of  the  throat  is  not  breai . 
ing;  it  merely  pumps  air  in  and  out  of  the  mouth.    When  air  is 
really  "  swallowed'"  the  sides  of  the  body  expand  and  the  floor 
of  the  mouth  rises.    Then  the  expired  air  is  forced  back  into  the 
mouth  where  the  constant  pumping,  above  mentioned,  gradually 


P.U.    FVknoMARY    ARTERY 
»•     FETROOUCTIVL     O«»»N« 
T*.     TRACHEA 


FIG.  9 1 a. 

replaces  it  with  fresh  air,  which  is  then  swallowed  and  the  process 
repeated. 

Considerable  blood  is  aerated  by  the  capillaries  in  the  skin, 
which  act  as  a  sort  of  gill,  obtaining  dissolved  oxygen  when  the 
animal  is  under  water.  This  is  an  evident  adaptation  for  its 
amphibious  life. 

Nervous  System.  The  nervous  system  shows  considerable  ad- 
vance over  that  of  the  fish.  The  cerebrum  is  larger  compared  with 
the  other  brain  parts.  The  brain  as  a  whole  is  more  specialized 


262 


BIOLOGY  FOR  BEGINNERS 


and  more  nearly  fills  the  cranial  cavity  of  the  skull;  while  the 
spinal  cord  is  shorter,  thicker,  and  has  its  branches  arranged 
much  more  like  those  of  the  higher  animals. 

Observation  of  the  living  frog  shows  that  all  the  senses  are 
fairly  developed  except  possibly  that  of  taste.    Sight  and  hearing 

ADAPTATIONS  OF  THE  FROG 


By  Means  of 


For  the  purpose  of 


External  features 
Head 


Limbs 


Digestive  organs 


Circulatory  organs 


Respiratory  organs 


Protective  color 

Shape,  and  slimy  secretion 

Large  mouth 

Location    and    shape    of 

tongue  and  teeth 
Nostrils  at  tip  of  nose 

Projecting  eyes 

Short  fore  limbs 
Long  hind  legs 
Very  long  feet  and  toes 
Powerful  muscles 
Webbed  toes 

Gullet  and  mucous  glands 
Stomach  and  gastric  glands 
Intestine,  liver,  and  pan- 
creas 

Three  chambered  heart 
Veins 
Arteries 
Capillaries 

Blood 

Gills  in  tadpole 
Two  lungs  in  adult 
Lung  lining  cellular 
Rich  blood  supply 
Throat  and  body  muscles 
Thin  vascular  skin 


Escape  from  enemies 
Locomotion  and  escape 
Catching  food 
Catching  food 

Breathing  when  partly  sub- 
merged 

Vision    when    partly    sub- 
merged 

Landing  after  leaping 
Increasing     leverage     for 

leaping 

Leaping  and  swimming 
Swimming 
Swallowing 
Digesting  proteids 
Digesting  and  absorbing  all 

food  stuffs 

Forcing  blood  through  body 
Bringing  blood  to  heart 
Carrying  blood  from  heart 
Distributing  blood  to  the 

tissues 
Transportation     of     food, 

oxygen,  waste,  CO* 
Absorbing  dissolved  oxygen 
Absorbing  free  oxygen 
Increase  of  absorbing  area 
Carrying  oxygen ,  etc. 
Taking  air  into  lungs 
Additional  breathing  when 
submerged 


THE  FROG  AND  ITS  RELATIVES  263 

are  probably  good,  and  its  varied  life  on  land  and  water  necessarily 
presents  a  wider  range  of  experiences  and  hence  some  advance 
in  intelligence. 

Excretory  System.  Excretion  is  provided  for  by  a  pair  of  well- 
developed  kidneys  with  a  large  bladder.  Water,  uric  acid,  and 
other  nitrogenous  waste  are  removed  by  these  organs,  while  the 
lungs  and  skin  also  help  dispose  of  waste  matter,  particularly 
carbon  dioxide  and  water. 

Reproduction.  As  in  the  fish,  the  sexes  are  separate,  and  the 
reproductive  organs  are  easily  found  upon  dissection.  The  ovaries 
appear  as  masses  of  eggs,  the  size  depending  on  the  season  of 
year.  The  sperm  glands  of  the  male  are  small  oval  organs  near 
the  kidneys.  Both  sets  of  organs  have  coiled  ducts  which  eventually 
connect  with  the  posterior  part  of  the  intestine  (cloaca)  into 
which  the  bladder  also  empties. 

It  may  be  well  to  remember  that  in  the  frog  we  find  systems  of 
organs  adapted  to  perform  all  the  life  functions,  and  that  in  the 
higher  animal  forms,  few  new  structures  are  developed,  but  rather, 
these  are  carried  to  a  greater  complexity  or  perfection. 

The  following  list  illustrates  this  and  would  apply  in  general  to 
most  vertebrate  animals. 

1.  Digestive  system 

Mouth,  tongue,  teeth,  throat  cavity,  salivary  glands 
Gullet  and  stomach,  gastric  glands 
Intestine,  small  and  large,  rectum,  and  cloaca 
Liver  and  gall  sac,  pancreas 

2.  Respiratory  system 

Nostrils,  mouth  cavity,  glottis,  and  trachea 

Lungs,  air  cells,  and  capillaries 

Skin 

3.  Circulatory  system 

Heart,  auricles,  and  ventricle 
Arteries,  aorta,  etc. 
Capillaries,  and  veins 
Lymph  vessels,  and  spleen 


264  BIOLOGY   FOR  BEGINNERS 

4.  Excretory  system 

Kidneys,  and  their  ducts  (ureters),  bladder 
Lungs,  and  skin 

5.  Nervous  system 

Brain:  consisting  of 

Olfactory  lobes 

Cerebrum 

Optic  lobes 

Cerebellum 

Medulla 

Spinal  cord  and  nerves 
Sense  organs,  eye,  ear,  etc. 

6.  Supporting  system 

Skeleton,  bone,  and  cartilage;  ligaments 
Connective  tissue 

7.  Muscular  system 

Body  muscles,  tendons 

Muscles  of  internal  organs,  heart,  intestines,  etc. 

8.  Reproductive  system 

Ovaries  and  oviducts 
Spermaries  and  sperm  ducts 

COLLATERAL   READING 

General  Structure:  Economic  Zoology,  Kellogg  and  Doane,  pp.  1-13; 
Economic  Zoology,  Osborne,  pp.  356-374;  Biology  of  the  Frog,  Holmes, 
entire;  Types  of  Animal  Life,  Mivart,  pp.  96-122;  Forms  of  Animal  Life, 
Rolleston,  pp.  74-81;  Winners  in  Life's  Race,  Buckley,  pp.  70-88;  Rep- 
tiles and  Birds,  Figuier,  pp.  17-33;  The  Animal  World,  Vincent,  p.  25; 
Textbook  of  Biology,  Peabody  and  Hunt,  pp.  101-119;  The  Frog  Book. 
Dickerson,  pp.  171-185;  U.  S.  Fish  Commission  Report,  1897,  pp.  251-261; 
Zoology  Textbook,  Davenport,  pp.  325-348;  Familiar  Lifet  Matthews, 
pp.  1-56;  Talk  about  Animals,  pp.  151-154,  160-164;  Wilderness  Ways, 
Long,  pp.  75-87;  General  Zoologv,  Colton,  pp.  181-195;  Zoology  Textbook, 
Linville  and  Kelly,  pp.  327-347. ' 

SUMMARY 
Amphibia  (two  lives). 

Characteristics:    metamorphosis  direct  fertilization 

no  scales  larva  vegetarian 

three-celled  heart  adult  carnivorous 

fairly  developed  brain 


THE    FROG    AND    ITS    RELATIVES  265 

Representatives:    Frogs,  tree-frogs,  salamanders,  toads,  newts. 
Frog. 

External  Structure. 

1.  Shape,  irregular,  not  graceful. 

2.  Covering,  loose  smooth  skin,  absorbs  water. 

Adapted  for  protection  by  color  and  slime. 
Adapted  for  respiration  by  capillaries,  thinness. 

3.  Head  (no  neck). 

Nostrils  anterior,  connect  with  mouth,  valve. 
Mouth,  large  for  catching  insects. 

Tongue,  fixed  in  front,  two  tips,  sticky. 

Teeth,  none  below,  small  on  upper  jaw  and  roof. 

Interior  structure. 

Nostril  openings  Eustachian  tubes 

Folded  tongue,  Gullet,  trachea. 

Eyes. 

Large,  projecting  as  protective  adaptation. 

Can  be  retracted,  three  lids. 
Ears,  flat  drum  on  surface  of  head. 

4.  Legs.     Anterior,  short  for  support  only. 

Posterior,  long,  strong,  for  leaping  and  swimming. 
Adaptations. 

Powerful  calf  and  thigh  muscles. 

Long  levers,  especially  ankle  and  toes. 

Webbed  toes.     Large  hip  bones. 
Comparison  with  man  (see  text). 

Legs  homologous  to  paired  fins  of  fish. 

Legs  homologous  to  legs  and  arms  of  man. 

Legs  and  fins  analogous  (locomotion). 

Legs  and  arms  not  analogous  (prehension  and  locomotion) 

5.  Muscles.     Spindle  shaped  as  in  higher  animals. 

Attached  to  bones  with  tendons. 
Not  in  separate  plates  like  the  fish. 
Internal  Structure. 
Digestion. 

'(  tongue,  attachment,  shape,  sticky. 
Food-getting  adaptations     -j  teeth,  upper  jaw  and  roof  of  mouth. 

I  mouth,  location,  size. 
Organs  of  digestion. 

Gullet,  short,  broad  (why?). 
Stomach,  oral,  diagonal,  covered  by  liver. 
Intestine,  medium  length,  coiled  (why?),  rectum. 
Glands,  salivary  and  mucous  in  mouth. 
Gastric  and  mucous  in  stomach. 

f  emptying  into  intestine. 
Pancreas  J 


266  BIOLOGY  FOR  BEGINNERS 

Essentials  for  digestive  system. 

Tubular  canal. 

Glands  for  secretion. 

Devices  to  increase  surface,  for  osmosis  absorption. 
Circulation. 
Heart,  location, 

Three  chambers,  two  auricles,  one  ventricle. 
Arteries,  carry  blood  from  the  heart. 

Carotid,  from  ventricle  to  head,  oxygenated  blood. 

Aorta,  from  ventricle  to  body,  oxygenated  blood. 

Pulmonary,  from  ventricle  to  lungs,  de-oxygenated  blood. 
Veins,  carry  blood  toward  the  heart. 

Portal-caval,  from  digestive  system  to  right  auricle,  de-oxygenated. 

Caval,  from  muscles,  etc.,  to  right  auricle,  de-oxygenated. 

Pulmonary,  from  lungs  to  left  auricle,  oxygenated. 
Blood  changes  in  lungs,  water,  carbon  dioxide,  out,  oxygen,  in. 
Blood  changes  in  kidneys,  water,  urea,  salts,  out. 
Blood  changes  in  liver,  impurities,  bile,  out,  sugar  changes. 
Advance  over  fish. 

Three-chambered  heart. 

Two  circuits  of  blood,  pulmonary  and  general. 

Lungs  instead  of  gills. 
Respiration. 

Gills  in  larval  stage,  lungs  later. 
Lungs,  shape,  location. 

Wall  structure,  air  cells,  and  capillaries  (why?). 
Action  of  lungs  in  breathing. 

Air  pumped  into  mouth  by  throat  and  swallowed. 

No  diaphragm  (cf.  man). 

Air  exchange  in  mouth,  nostrils  with  valves. 
Use  of  skin,  how  adapted  for  breathing. 
Nervous  System. 

Brain  larger,  specialized  parts,  nearly  fills  skull. 
Spinal  cord  thicker,  shorter,  with  specialized  branches. 
Senses  better  (Ex.  taste).     Higher  intelligence  (why?). 
Excretion.  Reproduction. 

Kidneys,  shape,  location.  Ovaries. 

function.  Sperm  glands. 

Lungs  and  skin.  Ducts. 

What  excreted  by  each. 


CHAPTER  XXDC 
THE  AMPHIBIA,   LIFE  HISTORY  AND  HABITS 

Vocabulary 

Caudal,  pertaining  to  the  tail. 

Cellular,  composed  of  cells. 

Obscured,  hidden. 

Hibernate,  to  remain  inactive  over  winter. 

Eject,  throw  out. 

Vicissitudes,  changes  and  accidents  of  life. 

Life  History.  The  life  history  of  a  frog  is  a  true  metamorphosis 
and  illustrates  perfectly  the  development  of  an  air-breathing  land 
animal  from  a  gill-using  aquatic  form. 

The  female  lays  the  eggs  in  the  water,  early  in  the  spring,  and 
they  are  fertilized  immediately,  thus  assuring  more  certain  develop- 
ment than  in  the  case  of  fish.  Each  egg  is  surrounded  by  a  jelly- 
like  coat  which  swells  in  the  water  until  all  are  joined  in  a  gelatinous 
mass.  In  this,  dark-colored  eggs  about  as  large  as  peas  can  be 
seen,  each  surrounded  by  a  transparent  covering.  The  rate  of 
embryo  growth  depends  somewhat  upon  temperature  and  food 
conditions  but  usually  the  parts  can  be  distinguished  within  each 
egg  in  less  than  ten  days.  The  little  tadpoles  themselves  leave 
the  mass  within  two  weeks. 

At  this  stage  they  fasten  themselves  to  stones  by  means  of 
sucking  discs  and  live  by  absorbing  the  attached  egg  yolk,  no 
mouth  being  developed.  There  are  three  external  gills,  a  narrow 
fish-like  body,  well  developed,  and  a  caudal  fin. 

Next  they  become  free  swimmers.  The  mouth  now  appears, 
and  a  very  long  coiled  digestive  tract  begins  work  on  the  vegetable 
scums  which  are  their  food.  Gradually  a  fold  of  skin  grows  back- 
ward over  the  gills,  like  an  operculum,  leaving  only  a  small  opening 

267 


268  BIOLOGY  FOR  BEGINNERS 

on  the  left  side.  This  has  an  internal  connection  to  the  right  gills 
so  that  both  are  supplied  with  water. 

These  latter  changes  may  have  occupied  nearly  two  months, 
and  the  tadpole  is  now  a  fish-like  animal,  with  gills,  lateral  line, 
fins,  two-chambered  heart,  and  one-circuit  circulation,  but  soon 
other  changes  follow,  gradually  adapting  the  aquatic  animal  for 
land  life. 

A  sac-like  chamber  develops  backward  from  the  throat  like  the 
fish's  air  bladder,  but  soon  separates  into  two  lobes  with  cellular 
walls  which  we  recognize  as  lungs.  To  correspond  with  this,  the 
circulation  is  gradually  modified;  the  gill  arteries  are  changed  to 
carotids,  pulmonaries,  and  aortic  arches;  the  heart  becomes  three 
chambered,  and  the  circulation  flows  in  two  circuits.  At  this 
stage  the  tadpole  may  be  seen  coming  to  the  surface  for  air  to  fill 
his  new  lungs  as  his  gills  no  longer  are  used  for  breathing  but  are 
being  modified  into  mouth  parts  and  other  organs. 

While  these  notable  changes  are  occurring  to  the  respiratory 
and  circulatory  systems,  others  no  less  remarkable  are  taking 
place  elsewhere.  The  mouth  widens,  teeth  develop,  and  the 
intestine  becomes  shorter  and  larger  to  adapt  it  for  animal  diet 
which  the  young  frog  now  begins  to  use. 

The  external  changes,  which  have  accompanied  these  last 
mentioned,  have  been  more  conspicuous,  though  less  important, 
and  are  as  follows.  The  tail  is  gradually  absorbed  (not  shed), 
limbs  develop  at  the  place  where  it  joined  the  body,  and  the  body 
itself  changes  shape.  The  front  legs  begin  growth  about  the  same 
time  but  do  not  show  so  soon  since  they  start  beneath  the  operculum 
in  the  gill  chamber  and  are  smaller  even  when  full  grown. 

By  this  time,  the  tadpole  is  a  well-developed  frog  which  comes 
on  land,  breathes  air,  eats  animal  food  and  gradually  grows  in  size 
till  he  reaches  the  full  stature  of  an  adult.  These  latter  changes 
have  occupied  usually  another  month,  making  a  total  of  about 
three  months  for  an  average  frog  metamorphosis,  though  growth 
in  size  may  continue  much  longer. 

Representatives.  Let  us  now  briefly  take  up  a  few  of  the  common 
representatives  of  the  amphibia,  which  includes,  besides  the  frog, 
the  toads,  salamanders,  newts,  etc. 


THE  AMPHIBIA,  LIFE  HISTORY  AND  HABITS       269 

Toads.  The  common  toad  is  a  much  abused  and  little  appre- 
ciated member  of  society:  he  suffers  from  many  false  accusations 
and  his  undeniably  plain  looks  have  obscured  his  many  virtues. 
To  begin  with,  toads  do  not  cause  warts;  they  do  not  "  rain  down  "; 
they  do  not  "  eat  their  tails  ";  and  they  are  never  "  found  alive 
in  solid  rock "  as  some  newspaper  scientists  would  have  us 
believe. 

On  the  other  hand,  the  toad  is  a  very  useful  and  interesting 
animal  and  makes  a  good  pet.  They  destroy  enormous  numbers 
of  harmful  insects,  though  we  seldom  see  them  in  action  as  they 
hunt  at  night,  when  their  prey  is  abundant  and  their  enemies, 
the  snakes,  are  asleep.  So  valuable  is  their  service  in  insect  de- 
struction that  in  Europe  toads  are  regularly  for  sale  to  gardeners 
and  others,  to  be  turned  loose  in  their  premises  to  protect  their 
crops. 

They  catch  their  food  with  the  tongue,  like  the  frog,  but  have 
no  teeth.  Their  rough  skin  and  dull  color  are  protective  in  their 
resemblance  to  the  earth  in  which  they  live.  They  can  change 
color  somewhat  to  match  their  surroundings  and  also  will  play 
dead,  to  escape  observation.  They  never  drink  water,  but  absorb 
it  through  the  skin  and  may  store  considerable  for  use  during 
winter  when  they  burrow  in  the  earth  and  hibernate.  It  is  this 
stored  water  that  toads  sometimes  eject  when  handled. 

They  burrow  rapidly  backwards  in  a  way  hard  to  understand ,  but 
very  efficient  and  will  bury  themselves,  in  a  few  minutes,  if  the 
ground  be  soft. 

They  breed  in  water  as  do  the  frogs,  but  spend  the  rest  of  their 
time  on  land.  They  also  differ  in  other  ways.  The  eggs  are  laid 
in  long  strands,  not  in  masses;  the  tadpoles  are  small  and  nearly 
black  and  develop  into  toads  at  much  smaller  size  than  do  frogs. 
They  emerge  from  the  ponds  in  thousands  when  about  the  size  of  the 
tip  of  your  finger  and  it  is  these  swarms  of  tiny  toads  that  give 
rise  to  the  idea  that  they  have  come  down  in  the  rain.  During 
the  breeding  season  they  develop  vocal  powers  of  no  mean  extent, 
their  song  being  a  rather  sweet  and  bird-like  trill. 

Their  eyes  are  even  more  handsome  than  the  frog's.    Altogether, 


270  BIOLOGY  FOR  BEGINNERS 

the  toad  is  a  useful  and  interesting  animal  and  should  never  be 
regarded  with  repugnance,  much  less,  with  enmity. 

Tree  Toads.  Another  member  of  the  amphibia  is  the  tree- 
toad  or  tree  frog  (Hyla)  which,  though  common,  is  seldom  seen, 
because  of  its  almost  perfect  protective  coloration.  Its  song 
however  is  familiar  enough  when  the  "  peepers'  "  cheerful  chorus 
ushers  in  the  early  spring.  They  vie  with  the  chameleon  in  ability 
to  change  color  to  match  their  surroundings,  green,  gray,  brown, 
yellowish,  and  even  purple  being  among  their  varied  disguises. 
It  seems  hardly  possible  that  so  loud  a  song  can  be  sung  by  a 
tiny  frog,  little  more  than  an  inch  in  length,  but  if  we  are  patient 
and  successful  enough  to  hunt  one  out  with  a  lantern  at  night, 
the  reason  is  clearer.  The  little  Hyla  can  expand  its  throat  into 
a  vocal  sac  twice  the  size  of  its  head,  and  with  this  enormous 
drum  can  produce  its  very  remarkable  music. 

They  are  true  tree  climbers  and  on  each  toe  have  sticky  discs 
by  which  they  can  climb  safely  on  the  bark  of  trees  and  even 
cling  to  glass.  Their  color,  stripes,  and  shape  protect  them 
perfectly  from  observation. 

The  eggs  are  laid  in  April;  and  the  tiny  reddish  tadpoles  feed 
on  mosquitoes.  The  adults  include  also  ants  and  gnats  on  their 
menu,  which  ought  to  give  them  a  place  in  our  affection.  A  curious 
fact  about  their  tadpole  stage  is  that  they  often  leave  the  water 
before  the  tail  is  nearly  absorbed,  being  apparently  able  to  breathe 
air  earlier  in  their  metamorphosis  than  do  most  other  frogs. 

Salamanders  and  Newts.  The  tailed  amphibians,  including 
salamanders,  newts,  and  mud  puppies,  are  less  known  than  they 
should  be.  We  have  over  fifty  species  in  the  United  States,  that 
being  more  than  are  found  in  any  other  country.  A  very  common 
mistake,  is  to  call  these  animals  "  lizards."  They  can  readily  be 
distinguished  because  a  lizard  is  a  reptile  and  has  scales  like  a 
snake  whereas  the  salamander  is  an  amphibian  and  has  a  smooth 
skin  like  a  frog. 

One  often  finds,  in  moist  woods,  tiny  brown  or  orange  red 
creatures  about  three  inches  long,  beautifully  spotted  with  scarlet 
and  black.  These  are  newts  and  very  curious  and  interesting  little 


THE  AMPHIBIA,  LIFE  HISTORY  AND   HABITS       271 

fellows  indeed.  They  can  only  live  in  moisture,  and  so  are  found 
after  rains  and  in  wet  places,  although  in  adult  form  they  breathe 
air.  They  have  the  regular  amphibian  metamorphosis,  though 
they  never  absorb  their  tails.  The  newt,  however,  adds  a  very 
curious  stage  to  its  life  history,  for  after  about  two  years  of  land 
life  it  returns  to  the  water,  even  from  great  distances,  changes 
color  to  olive-green,  develops  its  tail  fin  again  and  by  some  means 
is  enabled  to  breathe  the  dissolved  air  in  the  water.  Here,  after 
all  these  strange  vicissitudes,  breeding  takes  place,  eggs  are  laid, 
and  the  life  history  starts  again. 
The  true  salamanders  are  larger,  there  being  several  common 


FIG.  92.    The  western  brown  eft,  or  salamander,  Diemyctylus  torosus. 
From  Kellogg. 

species.  The  spotted  salamander,  black,  with  yellow  spots,  is 
about  six  and  one-half  inches  long,  and  the  black  salamander, 
blue  black  and  a  little  smaller,  are  two  of  the  kinds  most  often 
found  and  mistaken  for  lizards.  All  are  harmless  to  handle,  useful 
as  insect  eaters  and  so  helpless  and  interesting  that  they  ought 
never  to  be  destroyed. 

COLLATERAL    READING 

Metamorphosis:  The  Frog  Book,  Dickerson,  pp.  1-7;  Study  of  Animal 
Life,  Thompson,  p.  258;  Elements  of  Zoology,  Davenport,  pp.  451-457; 
Textbook  of  Zoology,  Packard,  p.  184;  Introduction  to  Biology,  Bigelow, 
pp.  389-414;  Lessons  in  Zoology,  Needham,  pp.  178-196;  Elementary 
Zoology,  Kellogg,  p.  299;  Biology  of  the  Frog,  Holmes,  pp.  81-119; 
Animal  Activities,  French,  p.  179;  Zoology  -Text,  Packard,  p.  874; 
Winners  in  Life's  Race,  Buckley,  pp.  70-77;  Cornell  Nature  Leaflet, 
Vol.  10,  No.  1,  pp.  88-97;  Life  in  Ponds  and  Streams,  Furneaux,  pp. 
360-399. 

Relatives:     American    Natural   History,  Hornaday,  pp.  359-374;    Frog 


272  BIOLOGY   FOR  BEGINNERS 

Book,  Dickerson,  pp.  53-239;  Elementary  Zoology,  Davenport,  pp.  325- 
348;  Practical  Zoology,  Davison,  pp.  199-211;  Elementary  Zoology,  Gallo- 
way, pp.  296-305;  Pet  Book,  Comstock,  pp.  246-259;  Handbook  of  Nature 
Study,  Comstock,  pp.  181-199;  Nature  Study  Leaflets  (bound),  pp.  185- 
206. 

SUMMARY 
Metamorphoses  of  Frog. 

Meaning  of  term,  other  examples,  tadpole  is  "frog  larva." 
Egg,  laid  in  water,  surer  fertilization,  in  spring. 
Gelatinous  protection,  parts  show  in  10  days. 
Tadpole  (attached  stage).  Discs,  three  external  gills. 

Lives  on  yolk.     Two  weeks. 
Tadpole  (free  swimmer),  mouth  develops. 

Long  intestine  because  vegetable  feeder  (explain). 
Lateral  line,  caudal  fin,  operculum  with  left  opening. 
Two-celled  heart,  fish-like.     Two  months. 
Tadpole,  frog. 

Mouth  widens,  intestine  shortens,  teeth  develop. 
Heart  three  celled,  arteries  change  from  gill  to  lung. 
Lungs  develop,  air  used,  skin  breathing. 
Tail  absorbed,  legs  develop.     One  month. 
Adult  frog. 

Total  time  about  three  months,  depends  on  food,  temperature,  etc. 
Representatives. 
Frog. 

Toad,  false  ideas,  real  value. 
Adaptations  for  food-getting. 
.  Tongue  as  in  frog,  no  teeth. 

Color,  skill. 
Distinctions  from  frog. 

Toad  Frog 

Eggs  in  strands  Eggs  in  masses 

Nocturnal  feeding  Daytime  feeding 

Tadpoles  small,  black  Tadpoles  larger,  lighter 

No  teeth  at  all  No  teeth  on  lower  jaw 

Rough  skin  Smooth  skin 

Tree  toad  (Hyla). 
Adaptations,  color  protection,  color  change. 

Discs  for  climbing,  vocal  sacs. 
Tadpoles  reddish,  early  develop  lungs,  eat  insects. 
Salamanders. 

Distinctions  from  lizards. 

Salamander  Lizard 

Common  Not  common 

Smooth  skin  like  frog  Scaled  skin  like  snake 

No  claws  on  feet  Claws  on  feet 

Metamorphosis  like  frog  No  metamorphosis 

Harmless,  useful  and  interesting. 


CHAPTER  XXX 

THE   REPTILES 

Vocabulary 

Iridescence,  changeable  rainbow  colors. 
Reticulated,  marked  with  a  network  pattern. 
Retracted,  drawn  back. 
Constrictors,  snakes  that  crush  their  prey  in  their  coils. 

There  is  probably  no  group  of  animals  less  understood,  and 
concerning  which  there  is  more  abundant  misinformation  than  the 
reptiles.  It  is  principally  to  correct  some  of  these  false  ideas  that 
they  are  discussed  here. 

The  reptiles  include  snakes,  turtles,  lizards,  and  crocodiles  and 


FIG.  93.    A  fence  lizard,  Sceloporus  occidentalis.    From  Kellogg 
and  Doane. 

the  points  in  which  they  differ  from  amphibians  are  as  follows: 
1 .   They  never  breathe  by  gills  at  any  stage. 
2    They  have  no  metamorphosis. 

3.  Eggs  are  internally  fertilized  and  have  a  shell,  or  young  may 
be  born  alive. 

4.  The  body  is  covered  with  scales. 

5.  Feet,  if  present,  are  provided  with  claws. 

273 


274  BIOLOGY  FOR  BEGINNERS 

False  Ideas  about  Snakes.  Of  all  the  reptiles,  the  snakes  are 
the  objects  of  more  ignorant  superstition  and  foolish  prejudice 
than  any  other  form.  To  begin  with,  snakes  are  not  "  slimy  " 
and  "  nasty."  Their  skin  is  as  clean  as  yours  and  feels  cold  merely 
because  of  their  lower  bodily  temperature.  Snakes  as  a  class  are 
absolutely  harmless  and  positively  useful.  Out  of  the  numerous 
species  inhabiting  the  United  States  only  the  rattler,  copperhead, 
moccasin,  harlequin,  and  coral  snakes,  are  dangerous  to  handle. 
Snakes  cannot  jump  from  the  ground  when  they  strike  nor  do 
they  spring  from  a  perfect  coil.  A  snake's  tongue  is  not  a  weapon 
nor  harmful  in  any  way.  It  is  an  organ  of  touch  only  and  is 
thrust  out  merely  to  feel  its  surroundings.  The  process  of 
death  is  slow  in  any  animal  with  a  low  nervous  organism,  and 
though  reflex  motions  persist  in  a  snake  long  after  death,  the 
setting  of  the  sun  has  absolutely  nothing  to  do  with  its  death. 
Snakes  do  not  swallow  their  young  to  protect  them;  "  hoop 
snakes "  do  not  roll  like  hoops;  horsehairs  do  not  turn  into 
snakes;  and  rattlers  do  not  add  one  rattle  per  year,  but  usually 
two  or  three,  though  some  may  be  broken  off.  Removal  of 
fangs  from  a  poisonous  snake  does  not  render  it  harmless  since 
other  teeth  take  their  place  almost  at  once.  Many  snakes  hiss; 
some  as  loudly  as  a  cat.  Most  snakes  can  swallow  prey  larger 
than  themselves.  All  snakes  are  muscular,  graceful,  and  usually 
swift  of  motion,  while  many  are  very  beautiful. 
I  "  There  is  no  living  creature  which  displays  such  a  beautiful 
pattern  of  colors  and  rainbow  iridescence,  as  the  reticulated 
Python  of  the  East  Indies,"  says  Wm.  T.  Hornaday. 

Children  are  not  born  with  any  natural  fear  of  snakes  and 
adults  should  never  be  allowed  to  terrify  their  minds  with  silly 
snake  stories  and  untrue  and  ignorant  statements. 

Adaptations.  Another  matter  which  is  little  appreciated  in 
regard  to  snakes,  is  the  fact  that  there  is  perhaps  no  other  animal, 
except  the  bird,  with  a  more  highly  specialized  structure. 

The  whole  animal,  but  particularly  the  head,  is  adapted  for  its 
peculiar  habit  of  catching  and  swallowing  prey  actually  larger  in 
diameter  than  its  own  body.  For  this  purpose  there  are  numerous 


THE  REPTILES  275 

sharp,  incurved  teeth  on  three  sets  of  jawbones,  any  of  which 
will  grow  again  to  replace  those  that  may  be  broken  or  torn  out. 
The  lower  jaw  is  not  fixed  directly  to  the  skull,  but  is  attached 
to  a  separate  bone,  the  quadrate,  which  in  turn  is  attached  to  the 
skull,  thus  permitting  the  jaw  to  move  forward  and  backward,  as 
well  as  up  and  down.  This  enables  the  snake  to  literally  crawl 
outside  of  its  victim,  the  upper  teeth  holding  firmly  while  the 
lower  jaw  is  advanced;  then  the  upper  jaw  takes  a  new  hold,  and 
so  on.  The  process  is  slow,  often  occupying  hours,  but  there  is 
no  chance  for  escape  of  the  prey.  The  snake's  teeth  cannot  bite 
the  food  in  pieces,  so  all  its  victims  must  be  swallowed  whole. 
To  permit  this,  the  various  bones  of  the  skull,  so  solid  in  other 
animals,  are  loosely  attached  in  the  snake,  allowing  the  head  to 
expand  when  swallowing  is  taking  place.  The  two  halves  of  the 
lower  jaw  are  attached  together  by  an  elastic  ligament  which 
allows  them  to  open  sidewise,  so  that  the  lower  jaw  is  capable  of 
three  motions,  up  and  down,  back  and  forward,  and  (each  half) 
sidewise. 

The  process  of  swallowing  is  so  long  that  special  adaptations 
are  provided  to  permit  breathing  to  go  on.  The  trachea  may  be 
extended  along  the  floor  of  the  mouth,  almost  to  the  teeth,  so  that 
air  may  reach  the  lungs,  and  moreover  there  is  a  large  air  chamber 
behind  the  lung  to  store  air  for  this  purpose. 

The  gullet  and  stomach  are  highly  elastic  and  the  digestive 
fluids  very  active,  to  accommodate  food  in  such  large  doses.  The 
flexible  ribs  and  lack  of  breast  bone  or  limb  girdles  allow  for  the 
passage  of  these  enormous  mouthfuls. 

The  delicate  and  slender  forked  tongue  is  protected  during 
swallowing  by  being  retracted  into  a  sheath.  Its  function  is  for 
touch,  rather  than  taste,  which  sense  would  be  of  very  little  use 
to  an  animal  which  eats  its  food  whole  and  sometimes  alive. 

Snakes  obtain  their  food  in  three  general  ways:  they  may  catch 
it  with  the  teeth  and  swallow  it  at  once  as  does  the  common  garter 
snake;  they  may  crush  the  prey  in  their  coils,  before  swallowing, 
as  do  all  constrictors ;  or  they  may  have  poison  apparatus  developed, 
which  stupifies  or  kills  their  victim  immediately. 


276  BIOLOGY   FOR  BEGINNERS 

Poisonous  Snakes.  While,  fortunately,  there  are  few  poisonous 
snakes  in  the  United  States,  their  adaptations  are  very  interesting. 
The  long  front  teeth  of  the  upper  jaw  are  either  grooved  or  hollow 
fangs,  moveable  in  some  snakes  and  fixed  in  others.  These  fangs 
are  connected  with  salivary  glands  which,  in  this  case,  secrete  the 
poisonous  venom,  and  are  so  arranged  that  the  act  of  striking, 
compresses  the  gland  and  forces  the  venom  into  the  wound  made 
by  the  fangs. 

In  common  with  most  ideas  about  snakes,  a  great  deal  of  non- 
sense is  current  regarding  the  frequency  and  deadliness  of  the  bite 
of  a  poisonous  species.  To  begin  with,  in  all  the  United  States 
the  annual  death  rate  from  snake  bite  is  about  two.  Second, 
all  snake  bites  are  not  necessarily  fatal.  Third,  unlimited  whiskey 
is  not  an  antidote. 

The  facts  of  the  case  are  about  as  follows,  summarized  from  two 
eminent  authorities,  Doctor  Stejneger  and  W.  T.  Hornaday. 

Learn  to  recognize  and  avoid  three  snakes:  rattlers,  copper- 
heads and  water  moccasins.  In  all  the  United  States  there  are 
but  five  poisonous  types,  and  the  three  mentioned  are  rare  except 
in  certain  localities.  The  rattlesnake  is  a  fair  fighter,  never  seeks 
trouble,  strikes  only  in  self-defense,  and  always  warns  before 
attacking,  so  that,  with  any  reasonable  care,  it  may  easily  be 
avoided. 

The  copperhead  goes  by  other  names,  sometimes  being  called 
the  "  pilot  snake  "  or  "  deaf  adder,"  and  as  it  attacks  without 
warning,  is  actually  more  dangerous  than  the  rattlers,  though 
slightly  less  poisonous.  It  is  usually  found  in  the  woods,  is 
seldom  over  three  feet  long,  and  is  beautifully  colored  with 
broad  bands  of  old  copper  on  a  background  resembling  new 
copper.  Any  snake  remotely  resembling  this  description  is  to  be 
avoided. 

Treatment  of  Snake  Bites.  Bites  are,  fortunately,  generally 
received  on  the  arms  or  legs,  and  are  not  necessarily,  nor  usually 
fatal  if  properly  treated.  Campers  in  snake-infested  regions  can 
obtain  for  five  dollars  or  less,  an  outfit  consisting  of  a  hypodermic 
needle,  chromic  acid  solution,  permanganate  of  potash,  and  liquid 


THE  REPTILES 


277 


strychnine,  which  with  the  anti- venom  serum,  now  easily  obtained, 
constitute  almost  sure  protection. 

POISON      APPARATUS       OP    i/VAKE. 


After  Linville  and  Kelly,  by  permission  ofGinn  and  Co. 

FIG.  94.    Poison  Apparatus  of  Snake. 

Fig.  1  shows  the  structure  of  the  skull.  Note  the  two  hinges  which  permit 
a  forward  and  backward  motion  of  the  quadrate  bone.  This  allows  the  lower 
jaw  to  be  extended  and  drawn  back  to  aid  in  swallowing  the  prey. 

The  very  loose  attachment  of  all  the  skull  bones  permits  great  freedom  of 
motion,  needed  when  swallowing  a  victim  larger  than  itself. 

The  fangs  are  grooved  or  hollow,  forming  an  outlet  for  the  poisonous  venom. 

Fig.  2  shows  part  of  the  head  dissected  away  to  expose  the  poison  gland  and 
the  muscles  that  press  upon  it  when  the  snake  strikes.  The  act  of  striking 
forces  the  venom  out  through  the  fangs,  into  the  wound. 

Fig.  3  is  a  diagram  showing  the  poison  gland,  duct  and  fang  removed.  Also 
the  secondary  fangs  which  develop  to  replace  the  large  ones,  if  they  are  in- 
jured or  torn  out  in  striking. 


278  BIOLOGY   FOR  BEGINNERS 

In  case  of  accident,  the  treatment  should  he  as  follows: 

1.  Cut  the  wound  to  promote  free  bleeding. 

2.  Tie  a  ligature  above  the  wound. 

3.  Use  anti-venom  serum  if  at  hand. 

4.  Give  alcoholic  stimulants  in  frequent,  small  doses:  an  excess 
may  cause  death. 

5.  If  no  serum  is  available,  inject  either  the  chromic  acid  or 
permanganate. 

6.  Inject  liquid  strychnine  (15-20  minims)  every  twenty  minutes 
until  spasms  begin. 

7.  Ligature  must  be  loosened  at  times  to  allow  the  circulation 
of  enough  blood  to  prevent  mortification. 

8.  Summon  a  doctor  if  possible,  but  it  is  the  treatment  of  the 
first  hour  that  counts. 

When  you  realize  that  only  about  two  in  over  100,000,000 
persons  die  of  snake  bite  in  the  United  States,  —  that  we  have 
few  venomous  kinds  of  snakes  in  this  country,  and  finally,  that 
rational  treatment  is  usually  successful,  you  can  see  how  foolish 
is  the  fear  and  hatred  so  often  shown  toward  these  really  useful 
and  handsome  animals. 

Solomon  selects  as  one  of  the  mysteries  of  nature,  "  the  way  of 
the  serpent  upon  the  rock  "  and  surely  their  adaptations  for  loco- 
motion are  peculiar  enough  to  warrant  this  distinction.  They 
have  no  legs,  yet  they  travel,  climb,  and  swim  with  ease  and 
rapidity.  They  accomplish  these  feats  by  means  of  the  broad  plates 
on  their  ventral  surface.  These  plates  have  their  free  edge  toward 
the  rear,  so  will  catch  against  the  slightest  roughness.  To  each 
plate  is  attached  a  pair  of  ribs  which  operate  somewhat  as  legs, 
with  each  plate  as  a  foot.  To  allow  free  motion  of  the  ribs,  the 
vertebrae  have  a  very  flexible  ball-and-socket  joint,  and  the  whole 
body  is  provided  with  exceedingly  strong  muscles,  so  that  a  snake 
really  travels  on  hundreds  of  muscular  legs  (ribs). 

This  is  a  good  example  of  analogy,  the  ribs  and  plates  perform- 
ing the  same  function  as  legs,  but  being  of  entirely  different  origin 
and  structure. 


THE  REPTILES  279 

COLLATERAL   READINGS 

Types  of  Animal  Life,  Mivart,  pp.  121-148;  Forms  of  Animal  Life, 
Rolleston,  pp.  67-73;  Winners  in  Life's  Race,  Buckley,  pp.  89-122;  Animal 
Life,  Thompson,  pp.  259-264;  Elementary  Zoology,  Kellogg,  pp.  303-326; 
Textbook  of  Zoology,  Linville  and  Kelly,  pp.  348-363;  Textbook  of  Zoology 
(elements),  Davenport,  pp.  349-369;  Textbook  of  Zoology,  Colton,  pp. 
196-207;  Lessons  in  Zoology,  Needham,  pp.  198-211;  Advanced  Text  in 
Zoology,  Shipley  and  McBride,  pp.  457-494;  Advanced  Text  in  Zoology, 
Parker  and  Haswell,  pp.  291-305;  Advanced  Text  in  Zoology,  Claus  and 
Sedgwick,  pp.  208-209;  Practical  Zoology,  Davison,  pp.  211-226;  Familiar 
Life  of  Field  and  Forest,  Mathews,  pp.  57-80;  Talks  About  Animals,  pp. 
155-159,  211-216;  American  Natural  History,  Hornaday,  pp.  313-353; 
Reptile  Book,  Ditmars,  entire;  Economic  Zoology,  Kellogg  and  Doane,  pp. 
260-272;  Reptiles  and  Batrachians  of  New  York,  Bulletin,  entire. 

-  SUMMARY 

Representatives. 

Snakes,  turtles,  lizards,  crocodiles,  and  alligators. 
Characteristics. 

No  metamorphosis  nor  gills. 
Eggs  internally  fertilized. 
Scales,  claws,  young  may  be  born  alive. 
Erroneous  Ideas. 

Not  dirty  nor  dangerous,  clean  and  useful. 
Reason  for  "cold  "  feeling.     Rattles  per  year. 
Tongue  for  feeling  only.     Fangs,  hissing. 
Reason  for  slow  death,  "hair  snakes,"  "  hoop  snakes." 
Adaptations. 

Food-getting,  methods. 

Caught  by  teeth  and  swallowed  (garter  snake). 

Crushed  before  swallowing  (boa  constrictors). 

Venom  to  kill  or  stupefy  (rattler,  cobra). 
Adaptations  for  food-getting. 

In-curved  teeth,  jaw  attachment. 

Elastic  skull  and  jaw. 

Tongue  sheath,  protrusible  trachea,  air  sac. 

Elastic  gullet,  strong  digestive  fluids. 
Adaptations  for  locomotion. 

Rib  attachment  to  ventral  plates. 

Ventral  plates  (scutes). 

Flexible  spinal  column. 

Analogy  between  legs  and  ribs. 
Poisonous  snakes. 

Apparatus,  fangs,  hollow  or  grooved  teeth. 

Fangs  movable  or  fixed. 

Poison  from  modified  salivary  glands. 

Muscles  for  ejection  of  venom. 


280  BIOLOGY  FOR  BEGINNERS 

Kinds. 

Rattle  snakes  (several  species)  known  by  rattle. 

Copperhead  (pilot  or  deaf  adder)  known  by  color. 

Water  moccasin  (found  in  southern  swamps,  large). 
Treatment  of  snake  bites. 

Promote  bleeding. 

Ligature  above  wound  if  possible. 

Use  serum  or  permanganate  of  potash  or  chromic  acid. 

Stimulate  with  little  alcohol  or  strychnine. 


CHAPTER  XXXI 

BIRDS,   THEIR   STRUCTURE  AND   ADAPTATIONS 

Vocabulary 
Flexible,  easily  bent. 
Impair,  to  interfere  with. 
Competent,  able. 
Concave,  curved  in. 

Eliminate,  to  excrete  or  throw  off,  as  waste. 
Coordinate,  to  make  to  work  together. 
Acute,  keen. 

The  group  of  birds  is  one  of  the  most  familiar,  useful,  and 
interesting,  of  all  the  animal  kingdom.  Among  the  vertebrates 
they  are  the  most  highly  specialized  in  structure,  every  organ 
being  adapted  for  the  one  object,  namely,  flight. 

Birds  are  sharply  distinguished  from  all  other  animals  by  the 
following  points,  among  many  others: 

1.  Their  body  is  covered  with  feathers. 

2.  Their  forelimbs  (arms)  are    developed  as  wings,  solely  for 
locomotion  and  never  for  prehension. 

3.  The  mouth  is  provided  with  a  horny,  toothless  beak. 

4.  The  body  is  supported  on  two  limbs  only  (like  man). 

Adaptations  for  Flight.  The  general  smooth  outline,  due  to  the 
thick  covering  of  feathers,  permits  easy  and  swift  passage  through 
the  air  with  little  resistance.  The  flexible  neck  and  legs  provide 
for  easy  "  fore  and  aft  "  balance,  while  the  wings,  being  attached 
high  above  the  bulk  of  the  body,  prevent  danger  from  tipping 
over  sidewise.  Lightness  is  secured  by  very  slender,  hollow,  air- 
filled  bones,  with  few  heavy  joints;  by  numerous  air  sacs  scattered 
through  the  body;  by  feathers  for  covering  and  locomotion;  and 

281 


282 


BIOLOGY  FOR  BEGINNERS 


by  having  teeth  replaced  by  the  light  but  strong  beak.  The 
chief  flight  adaptations,  however,  are  the  structure  of  the  feathers 
and  the  wing.  These  will  be  discussed  somewhat  in  detail. 


BIRDS,  THEIR  STRUCTURE   AND   ADAPTATIONS     283 


Feathers.  Feathers  are  modified  forms  of  scales  and  develop 
in  the  same  way  from  the  skin.  Some  unchanged  scales  are  always 
found  on  the  feet  and  legs,  which  remind  one  of  their  relationship 
to  reptiles.  They  are  not  evenly  distributed  over  the  bird's  body, 
but  are  found  in  certain  feather  tracts,  between  which  the  skin  is 
nearly  bare,  though  the  over- 
lapping feathers  do  not  re- 
veal it.  There  are  three 
kinds  of  feathers;  the  soft 
down  which  retains  bodily 
heat,  the  ordinary  body 
feathers  that  give  the  smooth 
and  graceful  outline  to  the 
otherwise  angular  form,  and 
the  large  quill  feathers  of 
the  wing  and  tail. 

These  latter  are  the  ones 
concerned  in  flight  and  con- 
sist of  a  broad  vane  spreading 
from  an  axis  (the  rachis) 
terminating  in  a  hollow  quill. 
The  vane  is  made  up  of  in- 
numerable rays  called  barbs, 
each  like  a  tiny  feather, 
having  projections  called 
barbules  (little  barbs)  which 
in  turn  are  held  together  by 
interlocking  hooks  of  micro- 
scopic size.  This  compli- 
cated arrangement  provides  a  vane  which  is  very  strong,  light, 
and  elastic,  and  furthermore,  if  the  barbules  become  unhooked 
as  when  a  feather  is  "  split  "  by  accident,  the  bird  merely  shakes 
them  or  draws  them  through  its  beak,  and  the  feather  is  whole 
again.  This  is  a  great  advantage  over  a  wing  membrane  such  as 
is  possessed  by  the  bats  which,  if  once  injured,  cannot  be  repaired. 

The  rachis  is  grooved  and  the  quill  hollow,  both  being  adapta- 


FIG.  96.     Structure  of  quill  feather. 


284  BIOLOGY    FOR   BEGINNERS 

tions  to  secure  greater  strength  and  less  weight.  At  the  base  is 
an  opening  through  which  nourishment  was  supplied  during  its 
growth.  The  vane  of  the  wing  feathers  is  wider  on  one  side  of  the 
rachis  than  the  other.  When  the  wing  strikes  against  the  air  it 
tends  to  turn  up,  but  rests  against  its  neighbor  and  is  held  flat, 
while  on  the  return  stroke  it  is  free  to  turn.  The  air  passes  through 
the  wing  as  each  feather  partly  turns  on  its  axis  ("  feathering  ") 
and  the  wing  meets  less  air  resistance. 

Uses  of  Feathers.  The  feathers  provide  the  means  of  flight, 
and  aid  in  easy  locomotion,  by  giving  the  angular  body  a  smooth 
outline.  Moreover  feathers,  being  one  of  the  best  heat-retaining 
substances,  serve  to  keep  the  bird  warm,  even  in  the  coldest 
weather,  no  matter  how  high  or  swift  its  flight.  Their  great 
activity  necessitates  their  high  body  temperature  and  the  feather 
covering  retains  this  heat  and  makes  possible  their  life  in  the  upper 
air.  The  feathers  of  most  birds  are  oiled  by  a  secretion  taken 
from  a  gland  near  the  tail  and  spread  on  them  by  the  beak.  This 
makes  them  waterproof  and  is  best  shown  in  swimming  and  diving 
birds,  which  can  spend  hours  afloat  and  suffer  no  discomfort. 

Feathers  have  a  further  use  in  providing  a  colored  covering 
which  helps  birds  in  escape  from  discovery  by  enemies  because  of 
its  resemblance  to  their  surroundings.  This  coloring  may  also  be 
used  to  attract  mates. 

Moulting.  Birds  shed  their  feathers  at  least  once  a  year,  so  that 
new  ones  may  replace  any  that  are  lost  or  damaged.  This  is 
especially  important  in  the  case  of  wing  feathers.  Some  species 
moult  twice  annually  and  may  have  differently  colored  plumage 
at  different  seasons.  This  change  of  color  is  sometimes  used  for 
protection  and  sometimes  to  attract  mates.  Wing  feathers  are 
shed  in  pairs  and  gradually,  so  as  not  to  impair  flight. 

SUMMARY  OF  USES  OF  FEATHERS 

1.  Flight. 

2.  Giving  regular  body  outline. 

3.  Protection  from  cold  and  water. 

4.  Protective  coloration. 


BIRDS,  THEIR    STRUCTURE    AND    ADAPTATIONS  285 


The  Wing.  The  wing  is  almost  as  wonderful  an  organ  as  the 
human  hand,  but  although  a  modified  arm,  it  has  lost  all  power  of 
grasping  and  is  adapted  entirely  for  flight.  The  shoulder  is  strongly 
braced  by  three  bones,  instead  of  two  as  in  man,  to  withstand  the 
tremendous  pull  of  the  powerful  muscles.  There  is  the  shoulder 
blade,  the  collar  bone  ("  wish  bone  "),  and  the  coracoid  bone  ex- 
tending to  the  sternum  (breast  bone).  All  three  are  devoted  to 
supporting  the  wing,  using  a  sort  of  tripod  arrangement,  which  is 
very  strong.  The  upper 

and   lower  arm   bones   are  ••*».»  a/wii 

long,  strong,  and  slender. 
The  wrist  is  lengthened  as 
are  also  the  fingers;  only 
three  are  present,  however, 
the  other  two  being  sacri- 
ficed for  lightness.  Thus 
we  have  a  long,  three- 
jointed  lever,  firmly  at- 
tached to  the  shoulder  with 
its  leverage  greatly  in- 
creased by  the  feathers.  The  problem  now  consists  of  providing 
the  necessary  muscle  to  swing  such  an  arm. 

Power  Required.  To  illustrate  the  difficulty  involved,  we  may 
take  as  an  example  the  pigeon.  It  weighs  about  a  pound  and  has 
a  wing  spread  of  about  two  feet.  This  would  mean  that  a  boy  or 
girl  of  ordinary  weight  would  have  to  swing  through  the  air  a  pair 
of  wings  each  from  fifty  to  seventy-five  feet  long  at  the  rate  of 
two  hundred  to  five  hundred  strokes  per  minute.  Try  to  swing 
your  own  arm  at  this  rate  for  a  minute,  and  then  imagine  the  power 
needed  for  a  wing  as  long  as  a  building  lot  front.  If  we  think  of 
keeping  up  this  form  of  exercise  for  forty-eight  hours  without  rest, 
we  will  have  some  idea  of  the  bird's  problem,  and  the  marvelous 
way  in  which  it  has  been  solved. 

Muscles,  competent  for  this  task,  could  not  be  located  on  the 
wing  itself,  as  that  would  too  greatly  increase  its  weight,  so  we 
find  the  breast  bone  enormously  enlarged  and  attached  to  it, 


FIG.  97.    Wing  structure  of  bird. 


286  BIOLOGY    FOR   BEGINNERS 

muscle  tissue  equal  in  some  cases  to  one-third  the  whole  weight 
of  the  bird.  To  connect  these  muscles  with  the  wing  bones,  a 
very  remarkable  set  of  tendons  pass  over  the  shoulder  joints  like 
ropes  over  pulleys  and  transmit  the  motion  to  the  wing,  much  as 
our  fingers  are  closed  by  muscles  located  in  the  forearm. 

Shape  of  Wing.  The  attachment  of  the  feathers  to  the  wing  is 
no  less  perfectly  adapted  for  its  purpose.  The  longest  feathers 
(primaries)  are  attached  to  the  fingers  where  their  leverage  will 
be  greatest.  Back  of  them  come  the  secondaries,  which  brace 
them  at  the  base  and  cover  the  spaces  between  their  quills.  These 
in  turn  are  further  supported  by  other  rows,  both  above  and  below. 
The  outline  of  the  wing  as  a  whole,  with  its  concave  under  surface, 
thick  forward  edge,  and  thin  flexible  rear  edge  and  tip,  has  just 
the  form  which  man  has  recently  discovered  best  for  his  aeroplane, 
and  is  beginning  feebly  to  imitate. 

Flight.  In  ordinary  flight  the  wing  stroke  resembles  horizontal 
figure  eight  —  down  and  back,  up  and  forward.  The  soaring  of 
birds,  like  the  hawk,  where  they  seem  to  fly  without  any  motion 
at  all,  is  not  understood.  It  may  be  due  to  slight  wing  motion, 
to  balancing,  or  to  utilization  of  wind  currents,  but  so  far,  man 
has  not  satisfactorily  explained,  much  less  imitated  it. 

When  man  flies  in  the  aeroplane,  of  which  we  are  so  proud. 
he  flies  not  like  the  bird,  with  beating  wings,  but  rather  like  the 
locust  or  beetle  with  stiff  planes  and  a  propeller  behind.  Thus 
far  we  have  no  engine  powerful  enough  to  swing  a  vibrating 
wing  machine,  large  enough  to  carry  a  man  in  flight  like  a 
bird. 

Muscles.  The  "  white  meat  "  of  a  chicken  is  the  mass  of  breast 
muscles  used  in  flight  and  the  large  breast  bone  with  its  projecting 
ridge  is  familiar  to  all  of  us.  This  ridge  gives  additional  room  to 
attach  the  powerful  muscles.  The  outer  layer  of  the  white  meat 
separates  easily  from  an  inside  portion,  this  latter  being  very 
tender.  The  explanation  is  that  the  outer,  larger,  and  tougher 
muscle  was  the  one  used  in  pulling  the  wing,  down  and  backward 
in  the  "  stroke  "  of  flying,  while  the  inner  and  more  tender  muscle 
acts  by  way  of  a  tendon  over  the  shoulder  to  raise  the  wing  for 


BIRDS,  THEIR  STRUCTURE  AND  ADAPTATIONS     287 

the  next  stroke,  a  much  easier  task  and  one  which  does  not 
toughen  it. 

Adaptations  for  Active  Life.  The  act  of  flight  requires  more 
work  than  any  other  form  of  locomotion.  This  is  shown  by  the 
enormous  breast  muscles  that  operate  the  wings,  and  the  general 
activity  of  the  bird's  whole  life.  Great  amounts  of  energy  are 
required  which  means  large  food-getting  and  digestive  ability. 
This,  in  turn,  demands  a  remarkably  complete  respiratory  system 
to  provide  for  rapid  oxidation  and  release  of  energy. 

Digestion.  Birds  are  provided  with  a  crop  for  storage,  a  gizzard 
in  which  small  stones  take  the  place  of  teeth  for  chewing,  and 
very  powerful  digestive  fluids,  all  of  which  work  together  to  care 
for  the  vast  amount  of  fuel  needed  to  run  so  powerful  an  engine. 
A  bird  usually  eats  several  times  its  own  weight  of  food  every  day, 
so  the  common  expression  to  "  have  an  appetite  like  a  bird  "  is 
hardly  a  suitable  comparison  for  a  light  eater. 

Respiration.  The  respiratory  organs  consist  of  very  finely 
cellular  lungs;  behind  these  are  the  air  sacs  which  hold  the  reserve 
air  and  permit  all  the  lung  tissue  to  be  used  in  supplying  oxygen 
to  the  blood.  These  air  sacs  also  aid  in  this  process.  The  rate  of 
respiration  is  very  high  and  the  normal  temperature  is  from  102 
to  no  degrees,  which  would  be  fatal  to  man  and  to  most  other 
animals.  Rapid  oxidation  means  rapid  production  of  waste 
matters  and  these  are  removed  largely  by  the  very  highly  developed 
lungs,  there  being  little  liquid  urine  eliminated  by  the  kidneys, 
and  no  sweat  glands.  Crystals  of  urea  are  excreted  by  the 
kidneys. 

Not  only  do  the  lungs  provide  the  blood  with  oxygen  for  oxida- 
tion, and  also  remove  waste,  but  in  addition  supply  the  air  for 
singing,  of  which  many  birds  require  a  large  amount.  It  might 
be  of  interest  to  mention  that  the  bird's  song  is  not  produced  in 
the  throat,  but  at  the  base  of  the  trachea  where  the  tubes  from  each 
lung  join.  Here  is  located  the  "  song  box,"  a  very  delicate  and 
highly  adjustable  structure. 

Circulation.  To  transport  this  large  burden  of  digested  food, 
oxygen,  and  the  waste  products  of  oxidation,  there  is  required  a 


288  BIOLOGY   FOR   BEGINNERS 

very  large  powerful  heart  and  well-developed  blood  vessels.  The 
rate  of  the  heart  beat  is  also  very  rapid. 

Other  Adaptations.  Since  the  bird  has  devoted  its  forelegs 
(arms  or  wings)  to  flight,  it  must  needs  balance  the  body  on  the 
other  pair,  a  thing  which  is  done  by  no  other  group  of  animals 
except  man.  As  an  adaptation  for  this,  the  legs  are  attached  high 
on  the  hips,  so  the  body  hangs  suspended  between  them  like  an 
ice  pitcher.  This  prevents  any  tendency  to  lose  balance  when 
walking,  and  permits  the  bird  to  bend  easily  and  to  pick  up  food, 
which  has  to  be  done  with  the  beak  since  the  fore  limbs  cannot 
be  used  for  prehension. 

Man,  although  he  can  balance  on  two  legs,  falls  easily  and  has 
to  learn  to  walk,  but  no  one  ever  saw  a  bird  fall  down,  or  have 
any  difficulty  in  walking.  The  difference  is  due  to  the  fact  that 
the  bulk  of  man's  body  is  above  the  point  of  support  at  the  hips, 
while  that  of  the  bird  swings  below. 

Perching.  The  bird  usually  perches  on  a  support  when  at  rest 
or  asleep  and  for  this  purpose  has  a  very  curious  arrangement. 
The  tendon  that  doses  the  claws  passes  over  the  leg  joints,  hence 
the  more  the  leg  is  bent,  the  tighter  the  claws  close  up.  Thus 
when  the  bird  settles  down  on  a  branch  to  sleep,  the  more  it  relaxes 
and  the  more  its  legs  bend,  the  closer  the  claws  grasp  the  perch. 
This  and  the  balancing  adaptations  enable  them  to  cling  to  a 
swinging  twig  when  awake,  or  to  a  perch  when  asleep,  with  no 
possibility  of  falling. 

Neck.  The  very  flexible  neck  is  another  adaptation,  especially 
for  food-getting,  since  the  wings  cannot  be  used  for  that  purpose. 
Not  only  is  the  bird  balanced  so  as  to  bend  easily  but  the  length 
of  the  neck  corresponds  to  that  of  the  legs;  because  of  this  the 
bird  can  always  reach  the  ground  to  pick  up  food. 

Feet.  The  feet  of  birds  differ  widely  in  structure,  depending 
on  the  particular  purpose  required,  and  are  a  splendid  example  of 
adaptation  in  themselves. 

The  common  perching  birds  have  three  toes  in  front  and  one 
behind.  Climbing  birds,  like  the  woodpecker  and  parrot,  have 
two  on  each  side,  while  swimming  birds  may  have  each  toe  with  a 


BIRDS,  THEIR  STRUCTURE  AND  ADAPTATIONS     289 

separtae  web  like  the  coot,  or  a  web  connecting  all  four,  like  the 
pelican,  or  only  the  front  three,  like  the  ducks  and  geese. 

The  birds  of  prey  (hawks,  owls,  and  eagles)  have  the  toes  provided 
with  powerful  claws  and  muscles  which  constitute  their  "  talons" 
for  catching  food.  While  at  the  other  extreme  are  birds  like  the 
swifts,  hummers,  and  whip-poor-wills,  which  have  very  tiny  and 
weak  feet,  since  they  live  on  insects  or  nectar,  and  spend  most  of 
their  time  in  the  air. 

Birds  which  wade  along  the  shores  in  search  of  food  have  long, 
slender  legs,  like  the  heron,  snipe,  crane,  and  plover,  while  in  diving 
birds,  such  as  the  loon  and  duck,  the  legs  are  so  short  and  so  far 
back  as  to  make  walking  very  awkward. 

Beaks.  Just  as  great  a  range  of  adaptation  is  shown  by  the 
beak  of  the  bird.  In  all  cases  it  is  light,  strong,  and  horny,  thus 
avoiding  weight.  With  each  class  of  birds  the  beaks  vary,  depending 
on  the  nature  of  their  food  and  the  manner  of  catching  it. 

The  hook-shaped,  strong  beak  of  the  hawk  and  owl  is  a  familiar 
adaptation  for  the  birds  of  prey  while  the  very  sharp,  chisel-shaped 
beak  of  the  woodpecker  enables  him  to  drill  deep  into  the  trees 
for  nest  holes  and  for  food.  Birds  like  the  swifts,  nighthawks,  and 
whip-poor-wills,  which  catch  insects  on  the  wing,  have  weak  but 
enormously  wide  beaks,  often  surrounded  by  hairlike  feathers, 
making  a  regular  trap  to  catch  their  food.  The  duck's  wide  beak 
with  toothed  edges  is  provided  for  scooping  food  from  the  mud 
and  straining  it  out  between  the  notches  when  the  head  is  shaken, 
while  the  slender  and  sensitive  beak  of  the  snipe  is  used  to  probe 
in  the  mud  for  single  pieces  of  food.  Parrots  use  their  short-hooked 
beak  for  defense,  food-getting,  and  for  climbing.  Sparrows  and 
finches  have  short  straight  beaks  for  crushing  seeds.  The  crossbill 
has  developed  a  real  pair  of  pliers  for  opening  cones,  which  contain 
the  seeds  he  eats,  while  at  the  other  extreme  is  the  humming  bird 
with  its  delicate  tubular  beak,  able  only  to  suck  the  nectar  of 
flowers. 

Nervous  System  and  Sense  Organs.  To  properly  coordinate 
and  control  so  complicated  and  highly  adapted  an  organism,  a 
well-developed  brain  is  necessary.  In  birds,  for  the  first  time,  the 


290 


BIOLOGY   FOR   BEGINNERS 


brain  completely  fills  the  skull;  the  cerebrum  is  broad  and  the 
cerebellum  especially  large,  as  is  to  be  expected  in  so  active  an 
animal. 


PAMMOT 


FIG.  98.     Bird  Beak  Adaptations. 

Hawk,  powerful,  sharp  beak  for  catching  prey. 

Woodpecker,  chisel  edged,  for  chipping  wood. 

Whip-poor-will,  weak  beak  but  wide  mouth,  surrounded  by  stiff  hairs,  for 
catching  insects  on  the  wing. 

Duck,  wide  beak  with  toothed  edges,  to  dig  up  mud  etc.  and  by  shaking  the 
head, 'sift  out  the  waste. 

Snipe,  slender  and  sensitive,  for  probing  after  food  in  the  mud  along  the 
shore. 

Parrot,  hooked  and  strong  for  climbing,  and  defense. 

Finch,  short  and  strong,  for  cracking  seeds. 

Cross-bill,  a  special  device  for  opening  cones  to  get  seeds. 

Humming  bird,  slender  to  suck  nectar  from  flowers. 

(After  Wright  and  Coues.) 

The  optic  lobes  are  also  well  developed  but  the  olfactory  (smell) 
lobes  are  usually  small  and  the  sense  of  taste  is  poor,  since  the  food  is 
swallowed  without  remaining  in  the  mouth  to  be  chewed  and  tasted. 


BIRDS,  THEIR  STRUCTURE  AND   ADAPTATIONS     291 

The  bird's  eye  is  a  very  wonderful  instrument,  the  sight  being 
keen  both  at  a  distance  and  for  close  vision,  and  the  change  of 
focus  is  very  quickly  made.  This  is  necessary  in  birds,  because 
they  must  see  clearly  to  pick  up  food  at  their  feet,  or  detect  an 
enemy  at  a  distance,  observe  their  prey  far  off,  or  weave  a  nest 
close  at  hand,  and  their  ability  along  this  line  is  unequaled  by  any 
other  animal. 

Their  hearing  is  usually  acute  though  there  are  no  external  ears, 
the  openings  being  protected  by  a  ring  of  feathers.  Keenness  of 
this  sense  is  useful  to  escape  danger  and  to  recognize  the  songs 
and  calls  of  their  mates. 

COLLATERAL    READING 

General  Structure:  Textbook  of  Zoology,  Parker  and  Haswell,  pp.  357- 
366;  Textbook  of  Zoology,  Shipley  and  McBride,  pp.  495-506;  Winners 
in  Life's  Race,  Buckley,  pp.  123-130;  Forms  of  Animal  Life,  Rolleston, 
pp.  46-66;  Textbook  of  Zoology,  Claus  and  Sedgwick,  pp.  232-238;  First 
Book  of  Zoology,  Morse,  pp.  174-180;  General  Zoology,  Colton,  pp.  208-221; 
General  Zoology,  Linville  and  Kelley,  pp.  364-373;  Elementary  Zoology, 
Davenport,  pp.  370-419;  Elementary  Zoology,  Needham,  pp.  211-237; 
Practical  Zoology,  Davison,  pp.  226-261;  Elementary  Zoology,  Kellogg, 
pp.  327-372;  Biology  Text,  Peabody  and  Hunt,  pp.  62-100. 

Flight  of  Birds:  Animal  Mechanism,  Pettigrew,  pp.  209-278;  Animal 
Locomotion,  Marey,  pp.  103-206;  Winners  in  Life's  Race,  Buckley,  pp. 
130-135;  Animal  Life,  Thompson,  pp.  123-124;  Textbook,  Shipley  and 
McBride,  pp.  501-502;  Introduction  to  Zoology,  Davenport,  pp.  310-311. 

Classification  and  Types:  Economic  Zoology,  Kellogg  and  Doane,  pp. 
273-294;  Birds  of  Eastern  North  America,  Chapman,  entire;  Bird  Life, 
Chapman,  entire;  Citizen  Bird,  Wright,  entire;  Textbook  of  Zoology, 
Linville  and  Kelley,  pp.  374-397;  General  Zoology,  Colton,  pp.  222-245; 
Types  of  Animal  Life,  Mivart,  pp.  66-95;  Little  Brothers  of  the  Air,  Miller, 
entire;  American  Natural  History,  Hornaday,  pp.  171-309;  N.  Y.  State 
Museum  Memoir,  Vols.  I  and  II,  entire;  American  Geographic  Magazine, 
bird  numbers,  entire;  Bulletins  of  U.  S.  Department  of  Agriculture;  Bulle- 
tins of  Audubon  Society;  Bird  Guides  (Land  Birds,  Water  Birds),  Reed, 
entire. 

SUMMARY 
Characteristics. 

Feathers,  wings,  beak,  two  feet,  shelled  egg. 
•1.    Adaptations  for  flight. 

Shape,  feathers  to  smooth  outline. 
Balance,  neck,  legs,  attachment  of  wings, 


202  BIOLOGY   FOR  BEGINNERS 

Lightness,  hollow  bones,  air  sacs,  feathers,  beak. 
Feathers. 

Origin,  modified,  scales  (other  epidermal  structures). 
Distribution,  tracts. 
Kinds,  down  for  warmth. 
Regular  feathers  for  outline. 
Quill  feathers  for  locomotion. 
Structure. 

(1)  Vane,  barbs,  barbules,  hooks. 
Advantages:  lightness  and  case  of  repair. 

(2)  Rachis,  grooved  for  strength. 

(3)  Quill,  hollow  for  strength  lightness. 
Shape,  one  sided  for  "  feathering." 

Uses,  flight,  contour,  warmth,  color,  to  shed  water. 
Moulting,  for  repair   replacement  and  color  change. 
Wing,  homologous  to  hand,  not  analogous. 
Bones,  three  shoulder  bones  in  tripod  form. 
Shoulder  blade,  narrow. 
Collar  bone  (wish  bone)  united. 
Coracoid,  to  breast  bone,  special  for  flight. 
Arm  bones  long  and  slender. 
Hand  reduced  to  three  fingers  (why?). 
Muscle  power. 

Muscles  not  on  wing  (why  ?),  cf.  human  hand. 
Breast  muscles  one-third  weight. 
Outer  and  inner  layers  (white  meat). 
Large  ridge  on  breast  bone. 
Tendons  and  pulleys  at  shoulders. 
Shape  of  wings. 

Feather  arrangement,  why  longest  feathers  at  end? 
Concave  below,  flexible  rear  edge  and  tip. 
2.   Adaptations  for  active  life. 

Much  energy,  oxidation,  food,  food-getting,  digestion,  respira- 
tion, circulation,  excretion. 
Digestion. 

Crop  for  storage,  flockwise  feeding. 
Gizzard  for  grinding  in  place  of  teeth  (why?). 
Powerful  digestive  fluids. 
Respiration. 

Lungs  finely  cellular  (why?). 
Air  sacs  for  reserve  air,  air  in  bones. 
High  rate  of  breathing  and  temperature. 
Excretion  via  lungs. 
Use  of  air  in  song,  location  of  syrinx. 
Circulation. 

Heart  large,  four  chambered,  rapid  beat. 
Blood  vessels,  large,  especially  to  breast. 


BIRDS,  THEIR  STRUCTURE  AND   ADAPTATIONS     293 


3.  Other  adaptations. 

(1)  Attachments  of  legs  for  balance  (cf.  man). 

Ease  of  picking  up  food,  since  no  hands  present. 

(2)  Perching. 

Tendon  action. 

(3)  Neck,  flexible  and  muscular  (why?). 

(4)  Feet. 


Structure  of  toes 

Examples 

Adapted  for 

3  front;  1  rear 

Song  birds 

Perching 

2  front;  2  rear 

Woodpecker 

Climbing 

Parrot 

All  webbed,  separate 

Coot 

Swimming 

All  webbed,  united 

Pelican 

Swimming 

Three  webbed,  united 

Duck,  goose 

Swimming 

3  front;  1  rear,  heavy  claws 

Hawk,  owl,  eagle 

Catching  prey 

Small,  weak 

Hummer,  swift 

Little  used 

Long  legs 

Crane,  heron 

Wading 

Legs  short,  far  back 

Loon,  duck 

Diving 

5.   Beaks.     (Why  not  teeth). 


Kinds 

Examples 

Adapted  for 

Hooked 

Hawk,  owl 

Catching  prey 

Chisel  shaped 

Woodpecker 

Drilling  in  trees 

Wide  but  weak 

Night-hawk 

Catching  insects  on  wing 

Swift 

Broad  and  notched 

Duck 

Scooping  and  straining 

Slender  and  sensitive 

Snipe 

Probing  in  mud 

Notched  and  hooked 

Parrot 

Climbing 

Short  and  thick 

Sparrows 

Seed-eating 

Crossed  mandibles 

Crossbill 

Opening  cones 

Slender  tube 

Hummer 

Sucking  nectar 

Nervous  system. 

Highly  developed  (why?). 

Brain  fills  skull. 

Cerebrum,  cerebellum,  and  optics  large. 

Taste  and  smell  not  acute  (why?). 

Sight  keen,  wide  range  of  focus. 

Hearing  keen  for  escape  and  recognition  (song). 


CHAPTER  XXXH 

BIRD  HABITS 

Vocabulary 

Unmitigated,  having  no  redeeming  feature. 
Excavated,  dug  out. 
Inaccessible,  hard  to  get  at. 
Stringent,  strict. 

Feeding.  As  before  mentioned,  their  intense  activity  requires 
that  birds  obtain  large  amounts  of  food.  Almost  every  thing  that 
can  be  eaten  comes  to  the  table  of  some  kind  of  bird,  certain  ones 
eating  animal  food  exclusively,  others  are  strict  vegetarians,  while 
many  use  a  mixed  diet. 

Among  those  using  animal  food  are  large  birds  of  prey,  such  as 
hawks  and  owls,  which  feed  upon  rats,  rabbits,  field  mice,  and 
other  small  animals,  also  upon  some  other  birds.  Then  there  are 
many  whose  diet  is  largely  or  entirely  fish,  which  they  catch  by 
diving,  as  do  the  loon,  grebe,  pelican,  and  kingfisher.  Some, 
like  the  vulture  and  buzzard,  are  scavengers  and  eat  any  dead 
animal  that  they  can  find;  such  birds  have  sight  very  keenly 
developed.  Probably  the  largest  number  of  birds  which  enjoy 
an  animal  diet  live  chiefly  on  insects  which  they  may  catch  on 
the  wing  (swifts),  by  burrowing  (woodpeckers),  from  the  ground 
(robins),  or  on  trees  (warblers). 

Many  birds  live  almost  exclusively  on  seeds,  doing  much  good 
by  the  destruction  of  weed  seeds  while  others,  such  as  blackbirds 
and  bobolinks,  do  considerable  damage  by  their  preference  for 
grain,  peas,  and  rice.  Various  kinds  of  both  wild  and  cultivated 
fruits,  especially  berries,  are  preferred  by  certain  birds  for  all  or 
part  of  their  bill  of  fare,  though  usually  the  fruit-eaters  have  to 
change  to  an  insect  diet  during  seasons  when  fruit  is  scarce. 

294 


BIRD   HABITS 


295 


It  sometimes  happens  that  birds  enjoy  the  same  seeds  or  fruits 
that  man  raises,  or  they  may  at  times  rob  his  yard  of  a  stray  chicken, 
but  very  careful  study  has  proven  that  there  are  but  three  or  four 
birds  which  do  more  harm  than  good.  The  rest  many  times  repay 
for  their  fruit  by  destruction  of  insects  and  vermin.  The  birds 
in  whose  favor  little  can  be  said  are  the  Cooper's  and  sharp-shinned 


FIG.  99.  Oriole's  nest  with  skeleton  of  bluejay  suspended  from  it, 
the  blue-jay  probably  came  to  the  nest  to  eat  the  eggs,  became  en- 
tangled in  the  strings  composing  the  nest  and  died  by  hanging. 
Photograph  by  J.  S.  Hanter.  (From  Kellogg.) 

hawks,  great  horned  owl,  and  English  sparrow.  The  verdict 
against  the  first  three  is  based  upon  their  destruction  of  poultry 
and  useful  birds,  while  the  sparrow  is  driving  away  many  of  our 
more  valuable  and  attractive  native  birds. 

The  English  sparrow  and  possibly  the  starling  also  are  examples 
of  the  unwisdom  of  tampering  with  the  balance  of  nature.  Both 
are  European  birds,  introduced  into  this  country  by  man.  Abroad 
they  are  not  over  numerous,  but  here,  removed  from  their  natural 


296 


BIOLOGY   FOR  BllGlXXLRS 


enemies,  they  multiply  unchecked  and  are  becoming  an  unmitigated 
nuisance. 

Nest  Building.  The  fact  that  the  bird's  egg  requires  continuous 
external  heat  for  hatching  is  a  point  in  which  they  differ  from  all 
lower  forms  and  necessitates  the  construction  of  some  sort  of  nest 
to  protect  the  eggs  and  retain  heat.  Next  to  migration,  the  highest 
development  of  bird  instinct  is  shown  in  some  of  their  nest  con- 
struction. We  must  remember 
that  they  have  no  hands  or  fore- 
limbs  to  help,  but  merely  beak 
and  feet,  and  their  materials  are 
only  such  as  they  can  find.  Y<i. 
when  the  wonderful  home  of  an 
oriole  or  humming  bird  is  studied, 
we  realize  that  even  with  hands, 
and  brain,  and  tools,  we  could  not 
imitate  them.  Nests  differ  widely 
both  as  to  materials  and  construc- 
tion. Earth,  clay,  sticks,  grass, 
hair,  feathers,  moss,  and  even 
strings  are  some  of  the  substances 
used,  while  the  structure  itself 
may  vary  from  a  mere  hole  in  the 
sand  (ostrich)  to  the  dainty  nest  of 
a  vireo. 

Excavated  Nests.  Water  birds 
often  lay  their  eggs  on  rocks,  with 
only  sticks  enough  to  keep  the 
eggs  from  rolling;  holes  in  the  ground  serve  for  kingfisher,  and 
bank  swallows,  while  owls  and  woodpeckers  excavate  homes  in 
hollow  trees. 

Woven  Nests.  Very  simple  grass  nests  are  made  by  ducks 
and  wading  birds.  Among  the  most  remarkable  woven  nests  are 
the  covered  pendant  homes  of  orioles  and  vireos,  hanging  from 
slender  limbs  where  no  thieving  cat  or  red  squirrel  can  come. 
Horsehair  and  plant  fibers  are  used  and  always  seem  to  be  so  well 


FIG.  100.  Nest  of  humming  bird, 
made  of  sycamore  down.  (One-half 
natural  size.)  From  Kellogg. 


BIRD  HABITS 


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298  BIOLOGY   FOR   BEGINNERS 

selected  and  woven  that  the  nest  often  withstands  the  storms  of 
several  seasons,  and  is  repaired  and  used  again,  frequently  by  the 
same  pair  that  built  it. 

Built-up  Nests.  Robins  make  a  clumsy  nest  of  clay,  lined  with 
grass  and  feathers,  placed  on  the  big  branches  where  cats  easily 
reach  them.  Swallows  are  much  better  masons  and  build  clay 
nests  on  barns  and  cliffs,  which  are  very  strong  and  inaccessible. 
They  roll  the  clay  into  pellets  with  the  beak  and  build  the  walls 
a  little  at  a  time,  leaving  one  layer  to  dry  before  adding  more, 
lest  it  all  collapse.  The  chimney  swift  (which  is  not  a  "  swallow  " 
at  all)  builds  a  nest  of  sticks  held  together  by  a  sticky  saliva  which 
hardens  into  a  strong  glue.  It  is  used  in  China  to  make  a  sort  of 
edible  gelatine;  it  is  from  this  fact  that  come  the  stories  of  the 
"  edible  birds'  nests  "  of  that  far-off  land.  These  are  merely  some 
of  the  various  types  of  nests.  Each  species  of  bird  builds  its  <>\\  n 
peculiar  structure,  always  in  the  same  way,  of  similar  materials, 
and  in  the  same  kind  of  location.  Yet  there  seems  to  be  no  way 
in  which  one  generation  is  taught  to  build  like  its  ancestors,  and 
when  we  say  it  is  due  to  instinct,  we  have  not  explained  how  they 
learn  to  construct  such  perfectly  adapted  homes. 

Both  the  nest  building  and  the  incubation  (sitting)  are  usually 
done  by  the  female,  though  in  some  species  the  male  helps  in  both 
processes.  On  the  other  hand  the  cuckoo  avoids  either  task  by 
laying  her  eggs  in  other  birds'  nests,  where  the  young  cuckoos 
sometimes  crowd  out  their  foster  brothers. 

Eggs.  Reproduction  in  birds  is  by  means  of  eggs  as  has  been 
the  usual  method  in  all  animals  previously  studied,  but  the  size, 
structure,  and  care  of  birds'  eggs  place  them  on  a  higher  plane  of 
development.  The  development  of  birds'  eggs  requires  constant 
warmth.  This  necessitates  the  building  of  a  nest  and  the  constant 
care  of  the  parent,  neither  of  which  is  usually  required  in  lower 
animals. 

Structure.  The  egg  consists  of  the  actual  growing  point  or  germ 
spot  at  the  upper  side  of  the  yolk,  the  yolk  surrounded  by  the 
"  white,"  this  by  a  double  membrane,  and  this  in  turn  by  the  shell. 
The  germ  cell  is  fertilized  and  from  it  the  chick  develops,  The 


BIRD   HABITS  299 

yolk  and  white  both  furnish  food  for  the  developing  embryo, 
somewhat  as  does  the  endosperm  of  a  seed,  while  the  membranes 
and  shell  are  protective  coverings,  porous  enough  to  admit  air  to 
the  chick,  and  to  allow  the  discharge  of  carbon  dioxide.  Fertiliza- 
tion takes  place  in  the  ducts  leading  from  the  ovaries.  Cell  division 
goes  on  for  about  twenty-four  hours  and  then  ceases,  only  to 
recommence  in  case  the  egg  is  warmed  and  kept  at  proper 
temperature. 

As  the  tiny  egg  germ  passes  along  the  oviduct,  the  yolk  and  white 
are  added,  layer  by  layer;  these  layers  sometimes  separate  in  a 
hard  boiled  egg.  The  yolk  is  the  real  egg,  corresponding  to  that 
of  fish  or  frog,  while  the  white  and  shell  are  added  nourishment 
and  protection  somewhat  like  the  jelly  that  coats  the  frog  and  toad 
eggs. 

Decay  of  stored  eggs  is  caused  by  bacteria  that  pass  through  the 
pores  of  the  shell.  If  eggs  that  have  no  bacteria  in  them  (i.e. 
"  fresh  ")  are  sealed  air-tight  by  a  solution  of  water  glass,  they 
do  not  decay  as  no  bacteria  can  get  in.  If  eggs  are  kept  in  cold 
storage,  the  bacteria,  even  though  present,  do  not  develop  and 
the  egg  "  keeps  "  for  months  with  but  little  change. 

The  shape  of  most  eggs  is  oval,  for  two  reasons:  they  pack 
better  together  in  the  nest,  and  cannot  easily  be  rolled  out.  Try 
to  roll  a  bird's  egg  and  it  will  follow  a  circle  and  come  back  to 
about  where  it  started.  Eggs  of  birds  making  deep,  safe  nests 
are  not  so  oval,  partly  because  they  are  safe  without  this  adaptation. 

The  number  of  eggs  varies  with  the  amount  of  care  that  the 
parent  birds  can  give  the  young.  It  is  greatest  in  those  kinds, 
whose  young  receive  the  least  attention  and  which  try  to  shift  for 
themselves  early  in  life.  This  increases  their  chances  of  destruc- 
tion and  makes  necessary  more  eggs  if  any  are  to  survive.  In  case 
of  birds  that  are  helpless  when  hatched  and  are  fed  and  protected 
by  parents,  the  number  is  lower.  Common  wood  and  field  birds 
average  about  five,  while  game  and  river  birds  have  twelve  or 
more;  on  the  other  hand  birds  of  prey  produce  but  one  or  two. 

The  size  of  the  egg  is  greater  in  those  species  which  hatch  well 
developed,  since  more  stored  food  is  required  to  carry  on  the  longer 


300  •      BIOLOGY  FOR  BEGIXXERS 

development.  In  all  cases,  however,  they  are  large  in  comparison 
with  eggs  of  other  animals. 

The  color  varies  greatly  and  is  probably  protective  in  some  cases 
where  nests  are  open  and  exposed.  On  the  other  hand,  eggs  laid 
in  burrows  and  deep  dark  nests  are  usually  very  white,  possibly 
to  make  them  more  visible. 

Use.  Since  the  egg  is  practically  a  store  of  food  for  a  young 
animal,  it  provides  an  especially  nourishing  and  concentrated 
form  of  human  food  which  has  been  used  by  man  for  ages.  Eggs 
require  no  cooking,  are  rich  in  proteid  and  fat  and  are  practically 
all  digestible.  The  egg  crop  of  the  United  States  is  worth  over 
$300,000,000  per  year. 

Incubation.  The  time  of  "  sitting  "  or  incubation  is  in  propor- 
tion to  the  size  of  the  egg  and  varies  from  thirteen  to  fifteen  days 
for  small  eggs,  to  forty  or  forty-five  days  in  the  case  of  the  swan. 
The  female  usually  sits,  but  the  ostrich  is  an  exception.  Some 
other  male  birds  help  in  the  incubation.  The  temperature  required 
is  105  degrees  and  must  be  kept  almost  constant.  In  birds  which 
are  helpless  and  have  parental  care,  the  incubation  begins  as  soon 
as  the  first  egg  is  laid,  and  the  chicks  hatch  one  after  the  other, 
but  in  those  birds  like  our  hens,  where  the  chicks  hatch  fully 
feathered  and  able  to  feed  themselves,  all  the  eggs  are  laid  before 
sitting  begins,  so  that  they  may  all  hatch  at  once. 

Bird  Migration.  One  of  the  most  mysterious  and  wonderful 
instincts  hi  the  world  is  that  which  controls  the  migration  of  birds. 
The  causes,  methods,  and  means  are  little  understood.  Many 
birds  never  migrate,  such  as  the  ostrich,  fish-eaters,  and  parrots. 
Crows,  owls,  jays,  woodpeckers,  and  many  others  are  practically 
permanent  residents. 

Migration  may  be  caused  by  food  supply,  climatic  changes,  or 
may  be  made  for  breeding  purposes.  It  is  not  easily  understood 
why  some  species  leave  abundant  food  and  warmth  in  the  tropics 
to  breed  in  the  cold  and  barren  North.  Insect  eaters  have  to  migrate 
as  whiter  kills  their  prey;  water  birds  must  leave  their  ponds 
before  they  freeze  over;  fruit  eaters  follow  the  season  of  their  diet 
to  some  extent,  but  after  all,  this  does  not  account  for  the  majority 
of  cases. 


Breeding 
Wintering 
Principal  migration  routes 


FIG.  101.   Distribution  and  migration  of  the  Eskimo  curlew.    (From  Cooke; 
Yearbook,  U.  S.  Department  of  Agriculture,  1914,  see  Pearse.) 


302  BIOLOGY  FOR  BEGINNERS 

Ducks,  hawks,  swallows,  and  swifts  migrate  by  night,  while 
warblers,  thrushes,  orioles,  sparrows  and  shore  birds  travel  by  day, 
thus  gaining  opportunity  for  day  time  feeding,  and  nights  for  rest 
and  protection.  The  distances  covered  are  enormous  and  could 
hardly  be  believed,  were  they  not  abundantly  verified.  Here  are 
some  examples  of  the  start  and  finish  of  their  journeys: 

The  bobolink  travels  from  New  York  to  Brazil 
* '    black  poll  warbler  from  Alaska  to  South  America     5 ,000  mi . 
"    night  hawk  "     Yukon  to  Argentina  7,000   " 

"    shore  birds  "     Arctic  regions  to  Patagonia  8,000   " 

"    arctic  tern  "     Arctic  to  Antarctic  circles  11,000   " 

This  last  is  the  champion  long-distance  traveller.  They  make 
the  round  trip  in  twenty  weeks. 

While  many  birds  migrate  slowly,  feeding  by  the  way,  and 
averaging  only  twenty  to  thirty  miles  per  day,  there  are  others 
which  are  marvels  of  speed  and  endurance.  Bear  in  mind  that  it 
is  considered  a  record  performance  to  drive  a  car  from  San  Francisco 
to  New  York,  2500  miles,  in  a  week  and  that  the  trains  require 
about  four  days.  Then  look  at  some  of  these  records. 

Gray-cheeked  thrush  travels  from  Louisiana  to  Alaska  in  thirty 
days,  a  distance  of  4000  miles. 

Golden  plover  travel  from  Nova  Scotia  to  South  America  in 
forty-eight  hours,  a  distance  of  2400  miles.  Over  the  open  ocean 
without  chance  for  rest,  this  bird  uses  two  ounces  of  its  fat  as  fuel 
for  the  whole  2400  miles.  Compare  this  with  the  fuel  used  in  the 
best  aeroplanes,  which  even  then  have  seldom  travelled  half  this 
distance  without  stopping.  The  tiny  humming  bird  has  a  record 
of  500  miles  per  night,  across  the  Gulf  of  Mexico,  and  then  is  not 
tired  enough  to  rest,  but  often  flies  on  inland  to  make  a  good 
trip  of  it. 

Routes.  Wonderful  as  are  birds'  speed  and  endurance,  a  real 
mystery  surrounds  their  knowledge  of  the  times  and  routes  for 
migration.  Similar  species  follow  the  same  routes  year  after  year, 
some  going  direct  over  the  ocean  (like  many  water  birds)  some 
follow  the  West  Indies  across  to  South  America;  many  cross  the 


BIRD   HABITS 


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Gulf  of  Mexico  directly  over  500  to  700  miles  of  open  water. 
Others  follow  the  coasts  or  river  valleys  and  may  even  go  by  one 


From  American  Museum  of  Natural  History. 

FIG.  102.    The  birds  carry  their  plumes  only  during  the  nesting  season; 
killing  the  parents  means  the  slow  starvation  of  the  young. 

route  and  return  by  another.  How  do  they  know  the  way?  Keen 
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They  do  not  seem  to  follow  water  ways  or  mountain  ranges  in 


BIRD   HABITS  305 

many  cases.  The  memory  and  leadership  of  old  birds,  though 
often  helpful,  cannot  account  for  migration  of  young  by  them- 
selves to  lands  they  have  never  seen.  We  have  to  assume  an 
instinct  of  migration  and  a  "  sense  of  direction  "  developed  to  a 
degree  that  we  can  only  imagine,  and  that  is  really  no  explanation 
at  all. 

Economic  Importance  of  Birds.  There  is  no  group  of  animals  to 
which  man  is  more  indebted  than  the  birds.  It  is  highly  probable 
that  without  their  aid,  agriculture  would  be  impossible,  because  of  the 
vast  quantity  of  insect  pests  and  weed  seeds  which  they  destroy. 
The  accompanying  table  shows  the  nature  of  the  food  which  they 
eat,  and  it  is  well  to  remember  that  they  eat  early  and  often. 

Their  greatest  service  is  in  the  destruction  of  harmful  insects 
both  as  egg,  larva,  and  adult.  In  some  states  where  general  bird 
killing  was  permitted  the  insect  enemies  of  crops  increased  to  such 
an  alarming  extent  that  stringent  laws  were  put  in  force. 

An  unwise  bird  law  cost  the  state  of  Pennsylvania  nearly  four 
million  dollars  in  a  year  and  a  half  through  the  destruction  which 
it  permitted  among  useful  birds.  At  the  end  of  this  period,  the 
damage  was  so  apparent  that  they  repealed  the  law  and  appointed 
a  state  ornithologist  to  look  after  the  birds.  Actual  experiments 
have  been  worked  out  with  protected  and  unprotected  bird  regions 
so  that  the  fact  of  their  essential  service  can  no  longer  be 
questioned. 

Next  to  their  destruction  of  harmful  insects  comes  their  work 
against  the  seeds  of  weeds  which,  as  the  table  shows,  constitute 
a  large  part  of  their  diet.  Many  of  the  larger  birds,  such  as  hawks, 
owls,  and  jays,  destroy  mice,  rats,  and  other  harmful  vermin. 
Some,  like  the  crow,  vulture,  and  buzzard,  act  as  scavengers. 

Almost  as  important  are  the  products  which  man  obtains  from 
the  birds.  Our  domestic  fowls  produce  flesh  and  eggs  to  the  amount 
of  over  half  a  billion  dollars  annually.  This  does  not  include  the 
value  of  game  or  wild  birds.  Feathers  for  millinery  and  bedding 
are  another  valuable  bird  product,  and  where  the  feathers  are 
those  of  food  birds,  it  is  a  perfectly  legitimate  one.  In  some 
Pacific  islands,  where  millions  of  sea  birds  have  roosted  for  centuries, 


306  BIOLOGY  FOR  BEGINNERS 

vast  deposits  of  manure,  called  guano,  have  accumulated,  which 
are  very  valuable  for  fertilizer. 

A  curious  and  rather  pitiful  use  for  birds  is  to  detect  poisonous 
gases  in  mines  and  in  warfare.  Their  rapid  respiration  and  delicate 
nervous  system  make  them  more  sensitive  than  man  to  the  presence 
of  dangerous  gases.  They  are  taken  in  cages  into  the  mines  or 
trenches  where  their  symptoms  of  suffocation  give  warning  in 
tune  for  the  men  to  take  precautions. 

Another  very  specialized  use  for  birds,  which  the  war  has  greatly 
developed,  is  the  carrying  of  messages  by  pigeons,  carefully  trained 
to  return  to  their  homes,  when  carried  to  the  front  and  liberated. 
Often  they  have  been  able  to  bring  back  messages  through  shell 
fire  where  no  man  could  live. 

Last,  but  by  no  means  least,  is  the  value  of  birds  to  man  as 
companions  and  pets.  If  the  world  were  deprived  of  all  bird  song 
and  color,  it  would  be  a  dreary  place,  and  even  those  who  now 
overlook  them,  would  miss  their  accustomed  presence. 

There  is  no  large  group  of  animals  with  so  few  harmful  members. 
The  food  table  indicates  a  few  which  destroy  fowls  or  useful  birds 
and  a  few  others  that  eat  grains  and  useful  fruits.  Another  class 
of  damage  is  in  cases  like  that  of  the  English  sparrow  and  starling 
where  a  foreign  bird  is  interfering  with  our  native  species.  The 
accompanying  "  Black  List "  includes  all  having  even  a  suspicion 
against  them,  and  shows  how  few  there  are,  which  do  any  harm 
at  all. 

Positively  harmful  Possibly  harmful 

Cooper's  Hawk  Blue  Heron 

Sharp  Shinned  Hawk  King  Fisher 

Pigeon  Hawk  Crow 

Great  Horned  Owl  Blue  Jay 

Snowy  Owl  Grackle 

English  Sparrow  Cow  Bird 

COLLATERAL   READING 

Migration:  Birds  of  North  America,  Chapman,  pp.  5-6,  13-20;  Bird 
Life,  Chapman,  pp.  48-61;  Travels  of  Birds,  Chapman,  entire;  Citizen  Bird, 


BIRD   HABITS  307 

Wright,  pp.  .63-72;  News  from  the  Birds,  Keyser,  pp.  139-149;  Wake 
Robin,  Burroughs,  pp.  1-35;  Bird  Migration,  Cooke,  U.  S.  Bulletin  185, 
entire;  see  also  magazine  references;  see  also  in  Encyclopedia,  under 
"Migration,"  "  Nidification,"  "Egg." 

Economic  Importance:  Our  Vanishing  Wild  Life,  Hornaday,  entire; 
Useful  Birds  and  their  Protection,  Forbush,  entire;  Our  Native  Birds, 
Lange,  pp.  64-98;  Birds  of  Eastern  North  America,  Chapman,  pp.  6-9; 
Textbook,  Kellogg,  pp.  370-372;  Birds  that  Hunt  and  are  Hunted,  Intro- 
duction; Birds  of  Field  and  Village,  Merriam,  introduction,  Chap.  XV, 
XXIV;  Textbook,  Davenport,  pp.  311-314;  Common  Birds  in  Relation  to 
Agriculture,  U.  S.  Bulletin,  entire;  How  the  Birds  Help  the  Farmer,  U.  S. 
Bulletin,  entire;  Bulletins  of  U.  S.  Department  of  Agriculture;  Pamphlets 
of  the  Audubon  Society,  etc.,  etc. 

Beaks  and  Feet:  Citizen  Bird,  Wright,  pp.  37-42;  Birds  of  Eastern  North 
America,  Chapman,  pp.  41-55;  Textbook  of  Zoology,  Kellogg,  pp.  362-364; 
Bird  Guide  (Water  Birds"),  Reed,  introduction. 

Life  History  and  Habits:  Handbook  of  Nature  Study,  Comstock,  pp. 
25-147;  Outdoor  Studies,  Needham,  pp.  47-53;  Winners  in  Life's  Race, 
Buckley,  pp.  168-180;  Ways  of  the  Wood  Folk,  Long,  pp.  27-120;  Familiar 
Life  in  Field  and  Forest,  Mathews,  pp.  81-111;  Upon  the  Tree  Tops, 
Miller,  entire;  Birds  in  the  Bush,  Torrey,  entire;  In  Nesting  Time,  Miller, 
entire;  Bird  Ways,  Miller,  entire;  Nature  Study  and  Life,  Hodge,  pp. 
305-364;  The  Pet  Book,  Comstock,  pp.  137-223;  Nature  Study  Leaflets 
(bound  volume),  pp.  253-290. 

Nesting  and  Eggs:  Bird  Homes,  Dugmore,  pp.  11-15;  Our  Native  Birds, 
Lange,  pp.  33-41;  Bird  Life,  Chapman,  pp.  64-70;  Citizen  Bird,  Wright, 
pp.  73-86;  News  from  the  Birds,  Keyser,  pp.  37-49;  Birds  of  Field  and 
'Village,  Merriam,  see  index;  Animal  Life,  Kellogg,  pp.  264-268;  Animal 
Life,  Thompson,  pp.  114-115,  264-267. 

SUMMARY 
Foods  used. 

Animal. 

Rats,  mice,  rabbits,  etc.  Hawks,  owls,  birds  of  prey. 

Fish  Loon,  pelican,  kingfisher. 

Scavengers  Vulture,  buzzard. 

Insects  on  the  wing.  Swifts,  night-hawks. 

Insects  under  bark  Woodpecker. 

Insects  on  the  ground  Robins. 

Insects  on  plants  Warblers,  vireos. 

Vegetable. 

Weed  seeds  Sparrows,  etc. 

Grains  (rice)  Blackbirds,  bobolink. 

Fruits  Wax  wing,  blackbird. 

General  value  of  birds. 
Harmful  exceptions. 

Cooper's  and  sharp-shinned  hawks,  great  horned  owl,  English  sparrow, 
and  starling  (why  so  numerous?). 


308  BIOLOGY  FOR  BEGINNERS 

Nest  Building. 

Necessity  for  nest,  warmth  for  egg  and  protection  of  young. 
Kinds. 

Excavated  in  earth  Kingfisher,  bank  swallow. 

Excavated  in  trees  Woodpecker,  owl. 

Woven  cup  shaped  Warblers. 

Woven  hanging  Orioles,  vireos. 

Built  up  of  clay  Robin,  eave  swallow. 

Built  up  of  sticks  Chimney  swift  (not  swallow). 

Eggs  (cf.  other  forms  of  eggs  as  to  size,  covering,  fertilization). 

Structure. 

Germ  spot  develops  embryo. 

Yolk  for  nourishment. 

White  for  nourishment. 

Membranes  Protection,  admit  air,  exit  CO2. 

Limy  shell  Protection,  admit  air,  exit  CO2. 

Causes  of  decay  and  means  of  prevention. 
Shape,  "  oval  "  for  better  fitting,  will  not  roll. 
Number,  fewer  where  more  parental  care  and  young  helpless. 

Larger  where  young  are  precocial,  average  five. 
Size,  larger  where  chick  hatches  well  developed. 
Color,  protective,  white  in  dark  nests. 
Use  as  food  for  man. 

Concentrated,  need  no  cooking,  all  digestible. 
Incubation. 

Small  eggs  less  time  (13-15  days),  larger  40-50  days. 

Female  usually  ''sits." 

Chicks  hatch  in  series  in  altricial  birds. 

Chicks  hatch  all  at  once  in  precocial  birds  (why?). 

Migration. 

Causes,  food  scarcity,  climatic  changes,  breeding. 
Methods,  night  fliers;  ducks,  hawks,  swallows,  etc. 

Day  fliers;   shore  birds,  warblers,  thrushes. 
Distances,  from  five  to  eleven  thousand  miles. 
Travel  in  flocks  for  protection  and  direction. 
Routes,  rather  definite,  along  coasts,  mountain  ranges,  etc. 

Not  known  how  they  direct  themselves. 
Examples  of  above  instances. 


BIRD  HABITS  309 


Economic  Importance. 

1.  Destroyers  of  harmful  insects. 

2.  Destroyers  of  weed  seeds. 

3.  Destroyers  of  harmful  rodents  and  other  vermin. 

4.  Scavengers. 

5.  Producers  of  food,  flesh  and  eggs. 

6.  Producers  of  feathers,  .bedding,  and  millinery. 

7.  Guano  for  fertilizer. 

8.  To  detect  poisonous  gases. 

9.  To  carry  messages. 

10.  To  furnish  enjoyment  by  their  beauty  and  songs. 

11.  A  few  destroy  useful  birds  or  other  animals. 

12.  Some  destroy  fruit  or  grain. 

13.  Some  interfere  with  nesting  of  other  birds. 

For  harmful  species,  see  "Black  List  of  Birds." 


CHAPTER  XXXIII 
MAMMALS 

Vocabulary 

Ruminant,  animals  adapted  for  re-chewing  their  food. 
Vertical,  straight  up  and  down. 
Quadrupeds,  four-footed  animals. 

The  mammals  constitute  the  highest  group  of  the  animal  kingdom 
because  in  them  the  development  of  the  brain,  intelligence,  and 
reason  have  reached  the  highest  degree  of  specialization. 

The  birds  excelled  in  adaptations  for  flight  and  in  marvelous 
instincts  for  nest-building  and  migration.  The  communal  insects 
have  carried  division  of  labor  to  a  remarkable  perfection,  but  if 
we  compare  the  real  intelligence  of  these  forms  with  that  displayed 
by  a  dog,  a  beaver,  or  a  horse,  not  to  mention  man,  we  can  see 
that  there  is  no  question  as  to  the  mammal's  position  at  the  top. 

Mammals  include  man,  the  apes,  quadrupeds,  bats,  seals,  whales, 
etc.,  and  are  a  very  diverse  group  as  the  tabulation  shows.  They 
vary  in  size  from  the  tiny  harvest  mouse  that  can  climb  a  wheat 
stem,  to  the  enormous  whale,  a  hundred  feet  in  length.  They  are 
found  in  all  parts  of  the  world  except  on  a  few  small  Pacific  islands 
and  are  the  group  of  animals  with  which  man  (himself  a  mammal) 
has  had  most  to  do. 

The  chief  characteristics  of  this  important  class  are  as  follows: 

1.  The  young  are  born  alive  (no  external  eggs). 

2.  The  young  are  nourished  with  milk. 

3.  The  body  is  more  or  less  covered  with  hair. 

4.  The  cerebrum  is  highly  developed. 

5.  A  diaphragm  (breathing  muscle)  is  present. 

6.  They  have  two  sets  of  teeth  and  fleshy  lips. 

7.  High  circulatory  development,  left  aorta  only. 

310 


MAMMALS  311 

Various  Adaptations.  Mammals  include  about  2500  different 
species,  which,  compared  with  insects  is  a  small  number,  yet  their 
habitat  and  mode  of  life  varies  so  widely  that  they  are  a  splendid 
illustration  of  the  modification  of  homologous  parts  for  different 
functions. 

Limbs.  All  mammals  have  two  pairs  of  limbs,  usually  provided 
with  five  toes;  some  are  modified  for  flight  (bats),  some  for 
swimming  (seals,  whales),  some  for  rapid  land  locomotion  (horse, 
deer),  some  for  climbing  (squirrel),  or  for  burrowing  (mole),  for 
attack  and  defense  (cat,  tiger),  for  jumping  (kangaroo),  for 
prehension  (apes,  man). 

Teeth.  In  the  same  way  the  teeth  may  vary  in  structure  and 
use,  there  being  usually  four  kinds  present,  the  incisors,  canines, 
premolars,  and  molars.  In  some  animals  they  are  adapted  for 
tearing  prey  (tiger,  lion),  some  for  gnawing  (rat,  beaver),  some  for 
grinding  vegetable  foods  (horse,  cow).  All  are  of  similar  origin 
and  are  merely  different  forms  of  the  same  organs. 

Body  Covering.  The  body  covering  also  varies  greatly.  The 
hairs  of  the  dog  or  horse,  the  wool  of  the  sheep,  the  quills  of  the 
porcupine  and  the  scales  of  the  armadillo,  are  all  of  similar  origin. 
Claws,  hoofs  and  nails,  horns,  bristles,  manes  and  tails  are  also 
developed  from  epidermal  structures. 

Four  Important  Orders.  The  mammals  of  North  America 
represent  eight  orders  out  of  eleven,  the  three  remaining  orders 
being  found  in  Australia  or  the  tropics.  From  this  number  we 
shall  study  only  four,  the  rodents,  ungulates,  carnivora,  and 
primates. 

The  Rodents  (gnawers)  include  many  of  our  commonest  animals, 
the  rabbits,  porcupines,  guinea-pigs,  chipmunks,  squirrels,  beavers, 
rats,  mice,  and  woodchucks.  All  these  forms  have  teeth  especially 
adapted  for  gnawing:  the  front  teeth  (incisors)  are  chisel  shaped, 
strong,  and  provided  with  a  continuously  growing  root,  so  that 
they  replace  themselves  as  fast  as  they  wear  off.  Also  the  front 
edge  is  harder  than  the  rear  edge,  so  that  they  are  self  sharpening 
since  the  cutting  edge  is  always  worn  thin.  These  tooth  adapta- 
tions together  with  strong  jaws  and  powerful  jaw  muscles  fit  the 


312  BIOLOGY  FOR  BEGINNERS 

rodents  for  their  well-known  occupation  of  gnawing  their  way 
through  life. 

The  Ungulates  (hoofed  animals)  include  some  of  our  commonest 
domestic  animals,  such  as  the  horse,  pig,  cow,  sheep,  and  goat. 
Among  its  familiar  wild  members  are  the  deer,  antelope,  tapir, 
rhinoceros,  hippopotamus,  giraffe,  camel,  zebra,  etc.  All  of 
these  most  of  us  have  seen  in  circuses  and  zoological  gardens. 
These  animals  live  on  vegetable  foods  and  have  back  teeth  (molars) 
fitted  for  grinding.  Most  of  them  have  a  side-wise  jaw  motion 
which  also  aids  in  this  process.  Their  feet  are  encased  in  hoofs, 
and  the  limbs  are  never  used  for  prehension,  being  adapted  only 
for  swift  locomotion.  There  are  never  more  than  four  toes  in  use 
and  frequently  fewer  are  developed. 

The  Ungulates  are  divided  into  two  groups: 

1.  Odd  toed  in  which  the  weight  is  borne  on  one  toe  though 
others  may  be  present.    They  include  the  horse,  rhinoceros,  and 
tapir. 

2.  Even  toed  in  which  the  third  and  fourth  toes  bear  the  weight, 
though  two  others  are  usually  present. 

These  even-toed  ungulates  are  again  divided  into  two  groups 
called 

1.  The  non-ruminants  (pig,  hippopotamus). 

2.  The  ruminants  (cow,  sheep,  deer,  etc.). 

The  ruminants  are  so  called  from  their  habit  of  chewing  their 
food  as  a  "  cud."  A  cow,  for  example,  first  compresses  its  food 
into  a  ball,  swallows  it  into  the  first  of  the  divisions  of  its  four- 
chambered  stomach  where  it  is  stored.  Later  it  is  forced  back  into 
the  mouth,  chewed  thoroughly  and  swallowed  again,  but  into 
another  stomach  chamber,  where  the  final  processes  of  digestion 
are  completed.  The  advantage  of  'this  peculiar  arrangement  is 
that  much  food  can  be  hastily  eaten  and  stored,  to  be  chewed  later. 
This,  for  an  animal  which  feeds  in  flocks,  on  bulky  vegetable  food 
is  of  great  importance,  since  it  can  get  its  share  in  haste  and  chew 
it  at  leisure.  The  ungulates  include  most  of  our  domestic  animals. 
From  them  we  obtain  the  bulk  of  our  animal  food  and  clothing, 
leather,  horn,  and  other  products  and  among  them  we  find  nearly 


MAMMALS 


313 


all  our  beasts  of  burden.    It  would  be  almost  impossible  for  man 
to  exist  without  this  important  group  of  animals. 

The  Carnivora  (flesh  eaters)  are  very  highly  specialized  in 
structure  for  the  pursuit  of  prey,  and  in  fact,,  live  largely  upon 
the  ungulates  whose  adaptations  have  been  along  the  line  of  keen 
senses  and  swiftness  to  escape  this  very  danger.  The  carnivora 
have  large,  interlocking  canine  teeth,  shear  cutting  molars,  a  very 
strong  jaw  hinge,  and 
enormous  muscles  attached  to 
ridges  on  the  skull.  Their 
skeleton  is  light  and  slender, 
the  jaw  short  and  strong,  and 
the  feet  usually  provided  with 
claws.  These  claws,  in  the  cat 
family,  can  be  withdrawn  into 
sheaths,  which  keeps  them 
sharp  and  also  permits  a  noise- 
less approach  upon  their  prey. 

On  the  other  hand,  the  dog 
family  cannot  withdraw  the 
claws,  which  are  therefore  blunt  and  not  used  for  prehension,  but 
for  swiftness  of  chase,  which  is  characteristic  of  their  manner  of 
hunting.  Their  keenness  of  sight  and  smell  have  been  especially 
adapted  for  their  manner  of  life. 

The  carnivora  include  two  divisions:  (1)  the  aquatic  forms  (seal, 
sea  lion,  walrus)  in  which  the  limbs  are  short  and  web-footed; 
(2)  the  land  forms  with  long  limbs  and  separate  toes.  These 
land  forms  are  divided  into  three  groups,  according  to  the  manner 
of  walking: 

1.  Those  walking  flat  on  the  foot  (bear,  raccoon). 

2.  Those  walking  on  the  toes  only  (dog,  wolf,  fox,  hyena,  cat, 
tiger,  lion,  leopard,  etc.). 

3.  Those  walking  partly  on  the  toes  (martin,  mink,  weasel,  otter, 
sable,  skunk,  etc.). 

It  will  be  noticed  that,  except  for  the  dog  and  cat,  none  of  the 
carnivora  are  domestic  animals,  and  few  of  them  are  used  as  food, 


FIG.  103.     After  Wiederscheim. 


314  BIOLOGY  FOR  BEGINNERS 

while,  on  the  other  hand,  most  of  our  valuable  furs  are  produced 
by  them. 

The  Primates.  This  group  includes  the  highest  of  the  mammals, 
and  comprises  the  monkeys,  gorilla,  chimpanzee,  orang-utan, 
gibbon,  marmoset,  and  lemur,  as  well  as  man  himself. 

Their  structural  adaptations  do  not  compare  with  those  found 
in  many  other  orders,  but  the  greater  brain  development  and 
intelligence  places  the  primates  at  the  head  of  the  classification. 

This  brings  up  again  the  fact  that  brain  development  is  the  only 
way  in  which  man  may  hope  to  excel.  He  belongs  to  what  is  called 
a  "  generalized  order  "  of  animals;  that  is,  he  is  not  structurally 
adapted  for  any  particular  thing,  such  as  flight,  speed,  strength, 
swimming,  etc.,  his  only  claim  to  distinction  being  along  the  line 
of  intellectual  development. 

There  is  nothing  that  man  can  do,  if  unaided  by  his  intelligence 
which  many  other  animals  cannot  do  much  better;  but  when  this 
intelligence  is  at  hand  to  direct  him,  there  is  no  other  animal  that 
can  compete  with  him. 

Structurally,  man  resembles  the  higher  apes  very  closely.  Al- 
most every  detail  of  their  anatomy  is  similar  —  skeleton,  muscles, 
teeth,  position  of  eyes,  structure  of  the  hand,  and  even  motions 
and  facial  expressions.  There  are,  however,  certain  structural 
differences  such  as  the  more  erect  position,  shorter  arms,  larger 
and  better-balanced  skull,  higher  forehead,  smaller  canine  teeth, 
and  his  inability  to  use  the  big  toe  like  a  thumb  for  grasping. 

These  differences  are  utterly  unimportant  when  compared  with 
the  one  great  feature,  the  human  brain.  The  brain  of  all  the 
primates  is  large  but  man's  is  one-third  larger  than  the  chimpanzee's 
which  most  nearly  approaches  it  in  size. 

Man  has  learned  the  use  of  tools,  devised  a  spoken  and  written 
language,  found  a  means  of  controlling  fire,  and  developed  mental 
faculties  and  social  habits  that  place  him  in  a  position  far  above 
the  highest  apes. 

It  is  curious  to  note  how  three  factors  have  contributed  to  man's 
development.  The  erect  attitude  left  the  fore  limbs  free  from  use 
in  locomotion  and  permitted  their  development  into  the  most 


MAMMALS  315 

wonderful  organ  of  prehension  in  the  world,  the  hand,  which  is 
man's  one  point  of  high  structural  adaptation. 

It  is  difficult  to  say  whether  the  brain  taught  the  hand,  or  the 
hand  helped  develop  the  brain,  but  it  is  certain  that  these  three 
factors,  erect  position,  hand,  and  brain,  have  been  the  essential 
ones  in  man's  development. 

There  is  more  structural  difference  between  the  lowest  primates 
(lemur)  and  the  chimpanzee  or  gorilla,  than  there  is  between  these 
higher  apes  and  man.  Also  there  is  a  greater  difference  between 
the  lowest  type  of  savage  man  and  the  highest  type  of  civilized 
man,  than  there  is  between  the  savage  and  the  ape. 

Results  of  Erect  Posture.  As  a  consequence  of  his  erect  posture, 
man's  hands  are  left  free  for  use  in  grasping  things.  However, 
nature  does  not  give  something  for  nothing,  and  man  has  to  pay 
for  his  upright  position  by  certain  disadvantages.  In  the  first 
place,  since  only  one  pair  of  limbs  are  used  in  locomotion,  he  must 
balance  upon  two  feet  instead  of  four,  and  has  the  center  of  weight 
high  above  the  point  of  support.  This  necessitates  the  long  and 
difficult  process  of  "  learning  to  walk  "  which  other  animals  do 
not  experience.  • 

Placing  the  weight  vertically  on  the  hips  instead  of  at  right  angles 
to  them,  renders  man  more  liable  to  hip,  spinal,  and  foot,  diseases 
and  deformities.  The  internal  organs  rest  one  upon  another  in  a 
vertical  pile  instead  of  lying  side  by  side,  producing  a  tendency 
to  pressure  or  displacement.  When  sick  or  tired  we  instinctively 
lie  down  to  relieve  this  strain. 

The  arteries  of  the  arm-pit,  neck,  and  groin  are  now  exposed 
toward  the  front,  whereas  in  quadrupeds  they  face  downward 
and  are  protected.  In  man,  the  trachea  and  appendix  open  up- 
ward, instead  of  forward,  giving  opportunity  for  the  entrance  of 
irritating  substances. 

All  these  difficulties,  which  are  the  price  of  our  erect  posture, 
are  more  than  repaid  by  the  advantage  of  the  human  hand  and 
the  mental  and  social  development  which  it  has  made  possible. 

It  rests  with  the  intelligence  of  man  to  overcome  the  natural 
difficulties  of  his  structure  by  especial  attention  to  correct  posture, 


316 


BIOLOGY   FOR  BEGINNERS 


position  of  spinal  column,  and  support  for  the  arches  of  the  feet. 
The  strain  on  the  internal  organs  can  be  met  by  training  the  ab- 
dominal muscles  to  support  their  extra  burden,  and  by  proper 
exercise  and  breathing.  All  this  is  but  a  small  price  to  pay  for  the 
human  hand. 

Relationship.  Contrary  to  the  ideas  of  some  ill-informed  people, 
no  scientist  has  ever  claimed  that  man  is  "  descended  from  "  an 
ape  or  any  similar  form,  neither  is  there  any  "  missing  link  "  to  be 
discovered.  On  the  other  hand  scientists  do  agree  that  both  man 


From  American  Museum  of  Natural  History. 

FIG.  104.  Brain  case  and  face  in  ape  and  man.  In  the  ape  (young  gorilla, 
at  the  left)  the  brain  case  is  comparatively  low,  and  the  face  is  shallow;  in 
man  (adult  white  man,  at  the  right)  the  brain  case  and  the  face  are  both  very 
deep;  the  face  has  been  retracted  beneath  the  brain  case.  Figure  after  Ritge. 

and  the  apes  are  descended  from  a  common  ancestor  from  which 
both  lines  have  developed.  This  accounts  for  the  very  great 
similarity  in  structure.  In  the  same  way,  we  resemble  our  cousins 
though  we  are  not  descended  from  them,  but  are  related  by  way 
of  a  common  ancestor,  or  grandparent. 
Aside  from  man,  the  primates  include: 

1.  The  gorilla,  the  largest  of  the  apes,  a  native  of  Africa.    It 
is  erect,  does  not  climb  trees,  and  resembles  man  closely  in  structure, 
though  much  stronger. 

2.  The  chimpanzee,  also  found  in  Africa.    Though  smaller  than 


MAMMALS 


317 


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318  BIOLOGY  FOR  BEGINNERS 

man,  it  resembles  him  more  closely  than  the  gorilla,  in  brain,  face, 
hands  and  ears. 

3.  The  orang-utan,  found  in  the  East  Indies,  which  also  re- 
sembles man  in  brain  structure  and  skeleton. 

4.  The  Old  World  monkeys  and  baboons  (Asia- Africa),  which 
have  narrow  noses  and  long  prehensile  tails. 

5.  The  New  World  monkeys  (South  America),  with  wide  flat 
noses  and  prehensile  tails. 

6.  Marmosets  (Mexico,  Brazil),  lemurs,   (Madagascar),  small 
forms,  not  at  all  like  man  in  structure. 

COLLATERAL   READING 
MAMMALS 

General  Zoology,  Colton,  pp.  246-285;  Textbook,  Linville  and  Kelly, 
pp.  408-435;  Elementary  Zoology,  Needham,  pp.  237-265;  Handbook  of 
Nature  Study,  Comstock,  pp.  212-307;  Practical  Zoology,  Davison,  pp. 
261-292;  Elementary  Zoology,  Galloway,  pp.  343-379;  Economic  Zoology, 
Osborne,  pp.  420-464;  Applied  Biology,  Bigelow,  pp.  436-453;  Economic 
Zoology,  Kellogg  and  Doane,  pp.  295-320;  Elementary  Zoology,  Kellogg, 
pp.  373-401. 

CARNTVORA 

Winners  in  Life's  Race,  Buckley,  pp.  279-314;  Familiar  Life  in  Field 
and  Forest,  Mathews,  pp.  112-244;  American  Natural  History,  Hornaday, 
Chap.  Ill;  Riverside  Natural  History,  pp.  353-479;  American  Animals, 
Stone  and  Cram,  pp.  207-285;  Life  of  Animals,  Ingersoll,  pp.  82-230; 
Textbook  of  Zoology,  Packard,  pp.  614-617;  Anatomy  of  Vertebrates, 
Huxley,  pp.  350-363;  Textbook  of  Zoology,  Claus  and  Sedgwick,  pp.  324- 
327. 

RODENTS 

Textbook  of  Zoology,  Linville  and  Kelly,  pp.  398-407;  Winners  in  Life's 
Race,  Buckley,  pp.  209-323;  Familiar  Life  in  Field  and  Forest,  Mathews, 
pp.  245-279;  American  Natural  History,  Hornaday,  Chap.  VII;  Riverside 
Natural  History,  pp.  68-81;  American  Animals,  Stone  and  Cram,  pp.  71- 
179;  Life  of  Animals,  Ingersoll,  pp.  404-468;  Talks  about  Animals,  pp. 
170-182;  Textbook  of  Zoology,  Packard,  p.  252;  Anatomy  of  Vertebrates, 
Huxley,  pp.  269-271;  Animal  Life,  Jordan,  Kellogg  and  Heath,  p.  71. 

UNGULATES 

Winners  in  Life's  Race,  Buckley,  pp.  256-279;  American  Natural 
History,  Hornaday,  Chap.  VIII;  Riverside  Natural  History,  pp.  233-352; 
American  Animals,  Stone  and  Cram,  pp.  28-70;  Life  of  American  Animals, 
Ingersoll,  pp.  231-385. 


MAMMALS  319 

PRIMATES 

The  Life  of  Animals,  Ingersoll,  pp.  7-57;  Riverside  Natural  History,  pp. 
480-500;  American  Natural  History,  Hornaday,  Chap.  II;  Animal  Life, 
Thompson,  pp.  340-350;  Types  of  Animal  Life,  Mivart,  pp.  1-35;  Winners 
in  Life's  Race,  Buckley,  pp.  240-255,  333-353. 

SUMMARY 

Mammals  excel  in  intelligence. 
Birds  excel  in  instinct  and  flight  adaptations. 
Insects  excel  in  "division  of  labor"  in  communal  forms. 
Mammals  vary  in  size  from  mouse  to  whale. 
Mammals  vary  in  distribution,  relatively  few  in  number  (2500). 
Characteristics. 

1.  Living  young,  egg  matures  internally.  4.   High  cerebrum. 

2.  Young  nourished  with  milk.  5.    Diaphragm. 

3.  Hair.     Fleshy  lips.  6.   Two  sets  teeth 

7.   High  circulation,  left  aorta. 
Modifications  of  limbs  (two  pairs,  five  toed). 
Adapted  for        .  Examples 

Swimming  Whale,  seal 

Flight  Bats 

Land  locomotion  Horse,  deer 

Climbing  Squirrel 

Burrowing  Mole 

Fighting  Cat,  tiger,  etc. 

Jumping,  Kangaroo  . 

Prehension  Man 

Modification  of  teeth  (incisors,  canines,  pre-molar,  and  molars) . 
Catching  prey  Lion,  tiger,  cat 

Gnawing  Beaver,  rat,  mouse 

Grinding  Horse,  cow 

Tusks  Elephant 

Modifications  of  body  covering. 

Hair  Dog,  horse,  man 

Wool  Sheep 

Quills  Hedgehog,  porcupine 

Scales  Armadillo 

Claws,  hoofs,  bristles,  tails,  manes,  etc.,  are  other  forms. 
Rodents. 

Representatives. 
Adaptations. 

Teeth  for  gnawing  (incisors). 

1.  Chisel  shape,  self -sharpening. 

2.  Strong,  powerful  jaws  and  muscles. 

3.  Continuous  growth  (why?). 

4.  No  canines. 


320  BIOLOGY  FOR  BEGINNERS 

Ungulates. 

Characteristics,  hoofed,  vegetable  food,  large  size. 
Limbs  for  locomotion  only. 
Not  more  than  four  toes. 
Odd  toed,  horse,  rhinoceros,  tapir. 
Even  toed. 

Non-ruminant,  pig,  hippopotamus. 

Ruminant,  cow,  bison,  sheep,  goat  (hollow  permanent  horns),  deer, 

elk,  moose  (solid,  shed  horns). 
Characteristics  of  ruminant  stomach. 
Reason  for  ruminant  habit. 
Value  to  man. 

Food,  meat,  and  milk,  with  all  related  products. 
Wool,  leather,  horn,  etc. 

Transportation,  horse,  ox,  camel,  mule,  llama,  etc. 
Carnivora. 

Specialized  for  pursuit  (ungulates  for  escape). 
Characteristics. 

Small  incisors,  interlocking  canines,  shear  molars. 
Strong  jaws,  jaw  muscles,  and  immovable  hinge. 
Light  strong  body,  keen  senses,  claws. 

Aquatic  forms  (short  limbs,  webbed  toes),  seal,  walrus,  etc. 
Land  forms  (long  limbs,  separate  toes). 
Plantigrade,  bear,  raccoon. 
Intermediate,  mink,  weasel,  otter,  skunk. 
Digitigrade  (claws  not  retractile),  dog,  wolf,  fox. 
Digitigrade  (claws  retractile),  cat,  lion,  tiger,  etc. 
Value  to  man. 

Few  for  food,  many  for  furs,  aid  in  chase,  enemies. 
Primates. 

Representatives,   gorilla,   chimpanzee,   orang-utan,    monkeys,    gibbons, 

lemurs,  man. 
Characteristics. 

Generalized  structure  (meaning).     Higher  brain. 
Man  resembles  other  primates  in 
Skeleton,  muscles,  teeth,  eyes,  hand,  habits. 
Man  differs  from  other  primates  in 

Erect  position,  shorter  arms,  balanced  head,  forehead. 
Smaller  canines,  non-opposible  toe. 
Brain  and  intelligence  which  results  in 
Tool  using,  fire  control,  language. 
Social  and  moral  development,  mind,  reason. 
Factors  in  nian's  development. 

Erect  attitude,  and  its  consequences. 
Hand  free  for  prehension. 
Brain  development  resulting  as  above. 
Relationship  of  man  and  other  primates  via  a  common  ancestry,  not  by 

"missing  links." 
(See  Hornaday  for  pictures  of  all  mammals,  especially  primates.) 


CHAPTER  XXXIV 
THE  DEVELOPMENT   OF   MAN 

Vocabulary 

Unwarranted,  uncalled-for. 

Rudimentary,  undeveloped  traces  of  organs. 

Fossil,  remains  of  former  plants  or  animals,  embedded  in  rocks. 

Evolution,  gradual  development,  from  simple  to  complex. 

With  an  egotism  which  is  entirely  unwarranted,  we  are  ac- 
customed to  speak  of  "  man  and  animals  "  whereas  we  ought  to 
say  "  man  and  other  animals,"  for  certainly  man  is  an  animal 
just  as  truly  as  the  beast  of  the  field. 

By  referring  to  the  characteristics  given  in  preceding  chapters, 
man's  place  in  the  zoological  scale  will  be  seen  to  be  as  follows: 

Kingdom:  animal. 
Branch:  vertebrate. 
Class:  mammals. 
Order:  primates. 

The  Idea  of  Evolution.  As  soon  as  man  became  intelligent  enough 
to  make  comparisons  between  himself  and  other  animals,  the 
resemblances  became  apparent  and  led  to  the  idea  that  some 
relationship  must  exist  with  lower  forms.  Two  thousand  years 
ago  the  Greeks  discussed  this  fact  and  advanced  various  theories 
to  account  for  it. 

Very  gradually,  information  accumulated,  and  the  idea  of  re- 
lationship developed  into  the  theory  that  not  only  man  but  all 
living  things,  both  plant  and  animal,  are  not  only  related,  but 
actually  descended  from  common  ancestors.  This  is  called  the 
theory  of  descent,  or  evolution. 

Evidences  of  Evolution.  1.  Rudimentary  Organs.  Not  only  do 
all  animals  resemble  each  other  in  general  ways,  but  many  forms 

321 


322  BIOLOGY  FOR  BEGINNERS 

possess  organs  which  are  of  no  use  to  them,  but  are  developed  in 
other  groups  for  important  functions. 

For  example,  in  the  foot  of  the  horse  there  are  unused  bones 
which  in  other  animals  support  separate  toes.  The  ostrich  has 
small  wings  like  those  of  other  birds,  but  it  cannot  use  them  for 
flight.  The  boa  constrictor  has  remnants  of  a  hip  girdle  though 
it  has  never  developed  legs  to  use  it. 

In  man  there  are  about  seventy  such  structures,  well  developed 
in  other  animals  but  reduced  in  size  and  function  in  his  body, 
like  remains  of  the  scaffolding  of  construction  left  in  a  completed 
building  and  showing  thereby  the  process  of  its  development. 
Among  these  may  be  mentioned  the  appendix  which  in  the  rodents 
is  the  largest  part  of  the  intestine,  while  in  man  it  is  reduced  to  a 
small  and  apparently  useless  rudiment.  Similarly  we  have  small 
canine  teeth,  but  do  not  develop  them  to  tear  food  like  the  dog; 
we  have  an  inturned  ear  tip  and  muscles  to  move  it,  but  we  do  not 
"  prick  up  our  ears  "  like  a  horse. 

The  list  might  be  greatly  extended,  but  the  point  is  this,  —  if 
animals  and  plants  are  not  developed  from  common  ancestors, 
why  then  do  they  have  these  resemblances  in  structure. 

2.  Embryological  Resemblances.  In  the  study  of  the  develop- 
ment of  the  embryos  of  all  animals,  it  is  found  that  the  higher 
forms  pass  through  stages  resembling  lower  types,  as  they  develop. 

The  first  stage  of  all  plants  and  animals  is  the  single  fertilized 
egg  cell.  In  all  cases  this  develops  by  almost  identical  steps,  into 
(a)  a  solid  mass  of  cells,  (b)  a  hollow  sphere  of  cells,  (c)  an  infolded 
tubular  form,  and  then  up  through  more  and  more  specialized 
structures  to  the  adult,  whatever  it  may  be.  The  early  forms  of 
all  vertebrate  embryos  are  so  similar  that  dog,  cat,  rabbit,  or  man 
cannot  easily  be  distinguished  until  well  started  toward  adult  form. 

By  watching  embryonic  development  of  the  vertebrates  we  can 
observe  modifications  of  various  structures,  such  as  the  gill  arches, 
which  are  present  in  all  the  early  stages.  These  gradually  develop 
true  gills  in  the  fish,  but  become  modified  and  reduced  in  the 
higher  forms,  their  rudiments  appearing  in  man  as  parts  of  the 
inner  ear,  lower  jaw,  and  throat  cartilages.  Certainly,  if  animals 


THE  DEVELOPMENT  OF  MAN  323 

were  not  related,  they  would  not  repeat  the  structure  of  lower 
types  as  they  develop  into  their  final  form. 

3.  Homologous  Organs.  In  both  plants  and  animals  we  find 
parts,  evidently  of  similar  origin  and  structure,  developed  for  very 
different  purposes. 

1.  Leaves  are  modified  into  petals  or  thorns. 

2.  Roots  act  as  organs  for  climbing  or  storage. 

3.  Hoofs,  nails,  and  claws  are  all  of  similar  origin. 

4.  Scales,  feathers,  and  hair  are  all  modified  forms  of  the  same 
epidermal  structures. 

5.  The  various  appendages  of  crayfish  and  its   relatives   are 
evidently  of  similar  structure,  but  modified  to  perform  many 
functions. 

Surely  this  modification  of  similar  parts  for  different  uses  would 
not  be  found  if  there  were  no  relationship  between  the  different 
forms. 

4.  Geological  Evidence..    Although  the  fossil  remains  are  neces- 
sarily incomplete,  still  there  have  been  found  many  series  showing 
gradual  development  from  primitive  to  present  forms.     This  is 
notably  true  of  the  horse  whose  ancestors  have  been  traced  in 
fossil  skeletons  back  to  a  small  five-toed  form  unlike  any  living 
representatives.    Also  in  the  case  of  birds  and  reptiles,  remains 
have  been  discovered,  showing  plainly  their  descent  from  a  common 
ancestor. 

5.  Domesticated    Animals    and    Plants.     We    are    continually 
witnessing  the  development  of  different  forms  of  plants  and  animals 
in  our  methods  of  breeding,  in  which  there  is  no  question  of  relation- 
ship of  the  new  form  to  the  old. 

Our  many  kinds  of  dog  are  descendants  from  the  domesticated 
wolf;  the  different  breeds  of  hogs  from  the  wild  boar;  fowls, 
pigeons,  sheep,  and  cattle,  with  their  numerous  breeds  and 
races,  have  been  developed  purposely  by  man,  from  very  different 
ancestors. 

From  masses  of  such  evidence,  laboriously  collected,  all  scientists 
are  agreed  that  all  living  things  are  related,  the  closeness  being 
indicated  by  the  degree  of  similarity.  They  also  agree  that  descent 


324 


BIOLOGY  FOR  BEGINNERS 


has  not  been  in  a  continuous  straight  line,  like  the  steps  upward 
in  a  ladder,  but  that  relationship  is  through  common  ancestors. 

We  have  certain  "  family  resemblances  "  to  our  cousins  but  we 
are  not  descended  from  them;  rather,  we  resemble  them  because 


EXISTING        GIBBON. 
APES  AND       Asia. 
MAN. 


MAN  CHIMPANZEE.      GORILLA.      ORANG. 

(Homo  sapient).          Africa.  Africa.          Asia. 

Asia,  Europe. 


Cro-Magnon  and 
other  races. 


More  primitive  spe- 
cies, human  and 
prehuman. 

Neanderthal  race. 

Piltdown  race. 
Heidelberg  race. 


GLACIAL  OB 
PLEISTOCENE 
AGE. 


Primitive  Gib- 
PLIOCENE     bon  of  Eu- 
AGE.  rope 

(Pliohylobatea).  Unknown  Pliocene 
ancestors  of  man. 


MIOCENE 
AGE.       Earliest  Gibbons 
of  Europe 

(Pliopithenu) . 


Ancestral  anthro- 
OLIGOCENE.  poids  of  Egypt. 

(Propliopiihecius). 


Unknown  ancestral  stock 
of  the  Old  World  pri- 

mates    including1  man. 


FIG.  105.  Ancestral  tree  of  the  anthropoid  apes  and  of  man. 
(From  Osborn's  Men  of  the  Old  Stone  Age.  By  special  permission 
of  the  publishers,  Charles  Scribner's  Sons.) 


of  our  common  ancestors  (grandparents),  who  contributed  to  the 
inherited  characteristics  both  of  ourselves  and  them. 

Proof  of  the  fact  of  descent  and  evolution  is  only  half  of  the 
battle;  it  remains  to  be  shown  how  nature  has  brought  about  the 


THE  DEVELOPMENT  OF  MAN  325 

great  modifications  which  have  resulted  in  producing  the  in- 
numerable forms  of  living  things  which  inhabit  the  globe* 


COLLATERAL   READING 

Primer  of  Evolution,  Clodd,  Chap.  IX-X;  Origin  of  Species,  Darwin, 
Chap.  14-15;  Descent  of  Man,  Darwin,  Chap.  1-7;  The  Whence  and  Whither 
of  Man,  Tyler,  pp.  1-112;  Applied  Biology,  Bigelow,  pp.  561-573;  Ascent 
of  Man,  Drummond,  pp.  59-98;  Animal  Life,  Thompson,  pp.  273-281. 


SUMMARY 

1.  Relation  to  other  animals. 

Classification,  look  up  characteristics  of  each  group. 

2.  The  idea  of  evolution. 

3.  Evidences  of  evolution. 

(1)  Rudimentary  organs. 

Toe  bones  of  horse. 

Wing  of  ostrich. 

Hip  bones  in  boa. 

Appendix,  canines,  etc.,  in  man. 

(2)  Embryological  resemblances. 

Beginning  with  one-celled  egg. 
Similar  early  stages. 
Modification  of  organs. 

(3)  Homologous  organs. 

(4)  Fossil  remains. 

(5)  Changes  due  to  domestication  and  breeding. 


CHAPTER  XXXV 
THE   METHOD   OF  EVOLUTION 

Vocabulary 
Isolation,  separation. 

Contemporary,  one  who  lives  at  the  same  time. 
Divergence,  separation  of  lines  of  descent. 
Predecessor,  one  who  comes  before. 

Proof  of  the  fact  of  similarity  between  the  various  forms  of  living 
things,  and  of  their  very  evident  relationship,  still  leaves  a  more 
difficult  question  to  be  answered.  How  did  this  descent  and 
modification  take  place,  by  what  means  has  nature  developed  one 
form  from  another? 

The  idea  of  evolution  of  living  forms  from  previous  simpler 
ones  had  been  in  existence  for  centuries,  but  the  first  serious 
attempt  to  explain  the  means  by  which  the  new  forms  evolved, 
was  made  by  Lamarck  in  1809.  He  advanced  the  view  that  new 
species  arose  by  inheriting  the  results  of  use  or  disuse  of  organs. 
For  example,  the  giraffe,  by  constantly  reaching  for  the  leaves  of 
trees,  developed  its  neck,  and  the  offspring  increasingly  inherited 
the  characteristic  until  a  new  species  was  formed. 

The  time  was  not  ripe  for  acceptance  of  Lamarck's  ideas; 
moreover,  his  theory  was  not  in  accordance  with  facts  and  was 
forgotten  for  fifty  years. 

Darwin's  Theory  of  Natural  Selection.  The  date,  1859,  marks 
an  epoch  in  biological  thought  and  should  never  be  forgotten.  In 
that  year  Charles  Darwin,  an  English  scientist,  published  his 
"  Origin  of  Species  by  Natural  Selection  "  and  established  the 
theory  of  evolution  on  a  firm  basis. 

This  theory  is  the  corner  stone  of  all  recent  science  and  the 
foundation  of  all  modern  thought.  It  is  not  confined  to  biology 

326 


THE  METHOD  OF  EVOLUTION  327 

alone,  but  has  influenced  almost  every  branch  of  science.  In  its 
broader  features  it  is  accepted  by  every  biologist,  although  there 
are  many  details  still  to  be  worked  out. 

Following  is  an  outline  of  the  chief  factors  assigned  by  Darwin 
to  account  for  the  development  of  new  species  from  common 
ancestry. 

1.  Over-production  of  individuals. 

2.  Struggle  for  existence. 

3.  Variation  among  individuals. 

4.  Survival  of  the  fittest. 

5.  Inheritance  of  favorable  characteristics. 

6.  New  forms  better  adapted  to  survive  are  thus  "  naturally 
selected  "  as  new  species. 

Darwin  spent  over  twenty  years  of  strenuous  toil  and  study, 
accumulating  facts  upon  which  to  base  his  theory.  Many  able 
men  have  since  devoted  their  lives  to  the  same  end,  but  we  can 
here  only  briefly  review  the  argument,  following  the  outline  given 
above. 

Over  Production.  A  fern  plant  may  produce  fifty  million  spores 
per  year.  If  all  matured  they  would  completely  cover  North 
America  the  second  year.  A  mustard  plant  produces  730,000 
seeds  annually,  which  if  all  matured,  would  occupy  two  thousand 
times  all  the  land  surface  of  the  earth,  in  two  years.  The  common 
dandelion  would  accomplish  the  same  in  about  ten  years. 

The  English  sparrow  lays  six  eggs  at  a  time  and  breeds  four 
times  a  year;  if  all  survived  there  would  be  no  room  for  any  other 
birds  in  the  course  of  a  decade.  The  codfish  produces  over  a 
million  eggs  per  year;  if  all  survived  this  would  fill  the  Atlantic 
solidly  with  fish,  in  about  five  years. 

Most  amazing  of  all  is  the  rapidity  of  reproduction  in  bacteria 
and  protozoa.  One  of  the  latter,  if  it  reproduced  unchecked, 
would  make  a  solid  mass  of  these  microscopic  animals  as  large 
as  the  sun,  in  thirty-eight  days. 

Struggle  for  Existence.  We  know  there  is  no  such  actual  in- 
crease; in  fact  the  number  of  various  forms  changes  but  little. 


328  BIOLOGY  FOR  BEGINNERS 

In  other  words  only  a  very  small  minority  of  these  countless  hosts 
reach  maturity.  All  cannot  obtain  either  space  or  food  to  live. 
Thus  it  is  evident  that  only  those  best  fitted  for  their  surroundings 
will  survive,  and  the  less  fit  will  perish  in  the  struggle. 

Variation.  It  is  a  well-known  fact  that  no  two  individuals  of 
any  plant  or  animal  are  exactly  alike;  slight  variations  in  structure 
occur  in  all.  This  furnishes  the  material  for  nature  to  use  in  her 
selection,  and  those  forms,  whose  variations  tend  to  adapt  them 
best  to  their  environment,  will  survive  while  others  perish. 

Survival  of  the  Fittest.  This  expression  was  first  used  by  another 
noted  English  scientist,  Herbert  Spencer,  and  almost  explains 
itself.  If  among  the  thousands  of  dandelion  seeds  produced,  some 
have  better  dispersal  devices,  these  will  scatter  to  better  soil, 
be  less  crowded,  and  so  will  survive,  while  those  having  poorer 
adaptations  will  perish  by  over  crowding.  In  so  severe  a  struggle 
where  only  a  few  out  of  millions  may  hope  to  Jive,  very  slight 
variations  in  speed,  or  sense,  or  protection  may  turn  the  scale  in 
favor  of  the  better-fitted  individual.  Any  unfavorable  variations 
would  surely  be  wiped  out. 

Inheritance.  It  is  common  knowledge  that  in  general,  the  off- 
spring resemble  the  parents.  If  the  parents  have  reached  maturity 
because  of  special  fitness,  those  of  their  descendants  which  most 
inherit  the  favorable  variation,  will  in  turn,  be  automatically 
selected  by  nature  to  continue  the  race. 

New  and  Better  Adapted  Species.  A  continuation  of  this  process 
of  natural  selection  will  in  time  produce  such  differences  in  structure 
and  habit  that  the  resulting  forms  must  be  regarded  as  new  species, 
genera,  and  finally  higher  groups.  This  process  is  aided  when  the 
developing  species  are  separated  by  distance,  mountain  ranges, 
bodies  of  water,  or  climatic  differences,  so  that  they  do  not  lose 
their  favorable  variations  by  inter-breeding.  This  is  the  theory  of 
geographic  isolation  which  was  developed  by  Alfred  Russell 
Wallace,  another  English  contemporary  of  Mr.  Darwin. 

Conclusions  from  the  Theory.  1.  Cause  of  Adaptations.  It  will 
be  seen  that  natural  selection  is  constantly  tending  to  fit  the 
individual  more  closely  to  its  environment  and  thus  accounts  for 


THE  METHOD  OF  EVOLUTION  329 

the  marvelous  adaptations  of  structure  which  we  always  find  in 
all  living  things. 

2.  Relationship  of  all  Forms.    Carrying  the  theory  to  its  logical 
conclusion  it  follows  that  all  the  species  now  on  earth,  or  which 
have  lived  there  in  the  past,  are  descended  from  a  few  primitive 
original  forms.    The  further  back  the  variation  began,  the  greater 
will  be  the  difference  between  the  present  forms,  and  the  more 
distant  will  be  then*  relationship.    Those  more  closely  allied  have 
separated  from  a  common  ancestor  in  more  recent  times. 

3.  "  Tree  "  Lines  of  Descent.    Evidently  our  idea  of  the  lines 
of  relationship  and  descent  must  be  expressed  in  the  figure  of  a 
tree,  whose  main  branches  separated  from  the  parent  trunk  early 
in  development  and  whose  topmost  twigs  represent  the  present 
living  forms.    These  will  be  similar  or  different,  depending  on  how 
far  back  the  divergence  began. 

4.  Classification.    Evolution  provides  for  a  natural  method  of 
classification,   now  universally  used,   in  which  relationship  and 
descent  are  shown  by  the  groups  in  which  individuals  are  placed. 

Thus  members  of  a  species  are  more  closely  related  than  those 
of  a  genus  or  order.  A  class  includes  forms  which  began  to  diverge 
further  back  than  the  members  of  a  family.  When  we  speak  of  any 
forms  as  "  belonging  to  the  same  order  "  or  genus,  we  are  really 
expressing  not  only  their  likeness  in  structure,  but  the  reason  for 
it,  namely  blood  relationship  and  descent  from  common  ancestry. 

5.  The  Key  to  other  Biologic  Puzzles.    Evolution  accounts  for 
many  facts  otherwise  unexplained.    It  tells  us  why  we  find  fossil   ! 
remains  of  simpler  animals  in  older  rocks,  and  of  more  highly 
specialized  forms  in  later  formations.     It  accounts  for  the  facts 
of  embryology  mentioned  in  the  previous  chapter,  such  as  the 
occurrence  of  primitive  structures  in  the  embryos  of  higher  forms, 
which  disappear  before  maturity.    It  explains  the  peculiarities  of 
geographic  distribution  of  animals  and  plants,  in  accordance  with 
what  we  know  of  past  and  present  relations  of  land  and  sea  areas. 

Some  Things  that  Evolution  does  Not  Teach.     1.   That  living 
or  extinct  forms  can  be  arranged  in  a  straight  line  of  descent,  each    ; 
descended  from  its  predecessor. 


330 


BIOLOGY  FOR  BEGINNERS 


Geological  History 


Period 


Characteristic  Animal* 


First 

Occurrence  of 


Mammoth. 

horse, 
Glyphodonts 


P/iocene 


Deer  Sloths. 
Ape .  Man 


Day  ,  Sta 

Came/. 

Ape .  Ma 


Elephant. 
Sabre-tooth 


CaT,    Bear. 

M  on  Hey. 

Cow ,  Deer. 


Crefaccous 


Mammals 

Birds . 
RcpTiles 


Marsupials . 
Salamanders 


Jurrass/c 


RepTiles 


Bird. 
Crocodile. 
Froq. 


Triable 


Reptiles  . 
Amphibians, 


Mam  ma/s. 
Turtles. 
Dinosaurs. 


Reptiles. 
Amphibians. 


Reptiles 


Devonian 


Fishes. 
Ostracoderms 


flyriapods 


Jr/urian 


Invertebrates 


fishes. 
Scorpions 


Invertebrates 


Bryozoans. 
Echinolds. 
Ophiurolds  • 


Cambrian 


Crustaceans. 
Molluscs. 
Worms  .etc. 


drachiopods. 
Tnlobites . 


rocks  -    no 


FIG.  106.     From  Pearse. 


THE  METHOD  OF  EVOLUTION  331 

2.  That  "  man  is  descended  from  a  monkey." 

3.  That  God  can  be  left  out  of  the  scheme  of  Creation.    Much 
opposition  was  made  to  Darwin's  work  on  this  score,  by  people 
who  purposely  or  through  ignorance,  misinterpreted  his  conclusions. 
While  we  cannot  go  into  the  argument  here,  rest  assured  that  in 
the  minds  of  the  greatest  scientists  and  philosophers  there  is  no 
conflict  between  the  conclusions  of  Science  and  Religion. 

To  quote  Davenport  "  The  Creator  is  still  at  work,  and  not 
only  the  forces  of  Nature,  but  man  himself,  works  with  God  in 
still  further  improving  the  earth  and  the  living  things  which  it 
supports." 

COLLATERAL   READING 

Origin  of  Species,  Darwin;  Descent  of  Man,  Darwin;  Primer  of  Evolu- 
tion, Clodd,  entire;  Evolution,  Thompson  and  Geddes,  entire;  Story  of 
Primitive  Man,  Clodd,  entire;  Evolution,  Coulter,  entire;  Ascent  of  Man, 
Drummond,  pp.  1-98;  Whence  and  Whither  of  Man,  Tyler,  pp.  1-112;  Win- 
ners in  Life's  Race,  Buckley,  pp.  333-353;  General  Biology,  Needham, 
Chap.  Ill;  Animal  Life,  Thompson,  pp.  273-339;  Applied  Biology,  Bige- 
low,  pp.  561-573;  Elementary  Zoology,  Galloway,  pp.  380-395;  Practical 
Zoology,  Davison,  pp.  342-354;  Elementary  Zoology,  Kellogg,  pp.  403-409; 
Economic  Zoology,  Osborne,  pp.  465-480;  Economic  Zoology,  Kellogg  and 
Doane,  pp.  335-347;  Elementary  Text,  Linville  and  Kelly,  pp.  101-115; 
Animal  Life,  Jordan  and  Kellogg,  pp.  114-148;  Animal  Studies,  Jordan, 
Kellogg  and  Heath,  pp.  281-289;  Elements  of  Zoology,  Davenport,  Chap.  21; 
article  on  "  Evolution"  by  Huxley  in  Encyclopedia  Britannica. 

SUMMARY 

1.  Evolution  idea  very  old. 

2.  Lamarck's  theory    of   the  inheritance  of  acquired  characteristics  not 

accepted;   not  now  considered  correct. 

3.  Charles  Darwin,  1859,  "Origin  of  Species  by  Natural  Selection." 

4.  The  theory  of  natural  selection,  to  account  for  origin  of  species. 

(1)  Over  production. 

(2)  Struggle  for  existence. 

(3)  Variation. 

(3)  Survival  of  the  fittest. 

(5)  Inheritance. 

(6)  Origin  of  better  adapted  forms. 

5.  Some  conclusions  from  the  theory. 

(1)  Accounts  for  adaptations. 

(2)  Indicates  relationship  of  all  forms. 

(3)  The  "  tree  "  line  of  descent. 


332  BIOLOGY  FOR  BEGINNERS 

(4)  Present  system  of  classification. 

(5)  Accounts  for  fossil  series. 
Accounts  for  embryo  repetition. 
Accounts  for  geographic  distribution. 

6.    Evolution  does  not  teach 

(1)  The  "ladder"  line  of  descent. 

(2)  The  man-monkey  descent. 

(3)  That  evolution  leaves  God  out. 

NOTE.  —  Darwin  did  not  originate  the  evolutionary  idea,  at  all,  as 
many  seem  to  think;  that  was  a  very  old  belief.  What  he  did  was  to 
prove  that  natural  selection  was  the  means  by  which  evolution  was  brought 
about.  There  are  doubtless  other  forces  assisting  natural  selection  in 
carrying  on  this  development,  some  of  which  are  fairly  well  understood. 


CHAPTER  XXXVI 

THE  DEVELOPMENT   OF  CIVILIZED   MAN 

Vocabulary 

Anthropology,  the  study  of  the  development  of  man. 
Diffidence,  hesitation. 
Obviously,  plainly. 
Relatively,  comparatively. 
Acquisition,  something  just  obtained. 
Degenerate,  less  developed  than  formerly. 

We  have  been  studying  the  development  of  living  things  and 
man's  relation  to  them,  which  brings  us  to  another  even  more 
fascinating  branch  of  biology,  the  development  of  man  himself, 
a  science  called  Anthropology. 

We  naturally  think  of  man's  development  in  terms  of  recorded 
history,  but  we  must  remember  that  writing  is  a  very  recent  art 
and  man's  actual  written  records  go  back  relatively  but  a  little  into 
the  far  past  from  which  we  are  still  emerging.  Greek  writings 
take  us  back  about  one  thousand  years  B.C.,  Chinese,  Egyptian, 
and  Arab  records  may  possibly  date  as  early  as  3000  B.C.,  but 
civilization  was  far  older,  and  man,  as  a  more  or  less  human  ani- 
mal, much  older  still.  Monuments  and  inscriptions  may  push  back 
the  boundary  by  vague  information  covering  perhaps  ten  thousand 
years,  though  there  is  much  dispute,  and  the  data  are  uncertain. 

Still  further  back  amid  the  mists  of  human  history  we  draw 
conclusions  from  bones  and  stone  implements,  showing  that  man 
existed  as  early  as  the  glacial  period,  and  was  contemporary  with  the 
cave  bear,  mammoth,  and  aurochs,  all  now  extinct.  One  ventures 
with  diffidence  to  set  a  time  in  years  for  the  date  of  these  remote 
ancestors  of  ours,  but  apparently  human  animals,  erect,  large- 
brained,  using  weapons  and  tools,  possessing  the  power  of  speech, 

333 


334 


BIOLOGY  FOR  BEGINNERS 


and  perhaps  the  use  of  fire,  existed  one  hundred  thousand  years  ago. 
Primitive  .man  apparently  had  a  much  smaller  brain  capacity 

than  his  modern  de- 
scendants, a  lower 
forehead,  sloping 
brow,  heavy  jaws,  and 
receding  chin.  Still 
he  was  obviously 
human  and,  even 
then,  intellectually  far 
superior  to  the  other 
Primates. 

His  earliest  home 
must  have  been  in 
relatively  warm 
climates  where  nature 
provided  food  and 
shelter  for  her  chil- 
dren too  ignorant  to  obtain  them  for  themselves.  His  food  was 
fruit  and  nuts  and  such  animals  as  he  could  capture,  unarmed, 


FIG.  107.  Vertebra  of  young  reindeer  with  flint 
arrowhead  imbedded  in  the  bone.  From  the  Cave 
of  Perigord,  France.  After  Lartel  and  Christy. 
See  Kellogg. 


FIG.  108.  Drawing  of  mammoth  on  piece  of  mammoth  tusk. 
From  the  Cave  of  the  Madeleine  in  Southwest  France.  The 
drawing  was  made  by  prehistoric  man  of  the  early  Post-Glacial 
times.  One- third  size  of  original.  From  Kellogg. 

and  eat  uncooked.     This  restricted  his  flesh  foods  mainly  to  clams 
and  oysters,  to  which  the  enormous  shell  deposits  still  bear  testi- 


THE  DEVELOPMENT  OF  CIVILIZED  MAN  335 

mony  in  many  places  in  central  Europe.  Evidently  man  soon 
devised  weapons,  clubs,  and  spears  perhaps,  and  later  bows  and 
arrows.  Then  he  became  a  wandering  hunter  having  no  fixed 
home  and  changing  his  abode  whenever  game  became  scarce  in 
any  one  locality. 

With  a  widespread  scarcity  of  game  came  the  necessity  of  taming 
and  raising  food  animals.  Thus  we  have  the  herdsman  wandering 
with  his  flocks  from  place  to  place,  as  pasturage  and  food  were 
exhausted.  Domestication  of  animals  probably  began  with  taming 


FIG.  109.    Remains  of  the  Neanderthal  man,  in  the  Provincial  Museum 
of  Bonn.    From  Weltall  u.  Menschheit,  see  Kellogg. 

the  wolf  to  aid  him  in  the  hunt,  but  the  real  progress  was  made 
when  tame  cattle,  sheep,  and  goats,  partly  took  the  place  of  wilder 
game. 

A  wonderful  advance  was  made  when  man  hit  upon  the  idea  of 
cultivating  food  plants  for  his  flocks  and  himself.  This  permitted 
a  fixed  habitation  and  for  the  first  time,  a  real  "  home  life  "  had  a 
chance  to  develop,  with  all  that  it  means  in  comfort  and  social 
progress.  Doubtless  the  house  was  but  a  cave  or  tree  shelter,  but 
when  man  settled  to  remain  in  one  place,  to  cultivate  and  gather 


336  BIOLOGY  FOR  BEGINNERS 

his  simple  crops,  community  life  and  society  had  their  earliest 
beginnings. 

Man's  development  is  usually  classified  by  the  implements  he 
had  learned  to  use. 

1.  Primitive  Man.     Without  weapons,  tools,  or  fire. 

2.  Old  Stone  Age.      Stone  weapons  and  tools,  probably  used  fire. 

Contemporary  with  mammoth  and  cave 
bear. 


FIG.  110.  Skull  cap  of  Pithecanthropus  erectus,  the 
fossil  man-like  ape  of  Java.  Shown  from  above  and 
in  profile;  from  Wei  tall  u.  Menschheit,  see  Kellogg. 

3.  New  Stone  Age.    Used  polished  stone  implements. 

Perhaps  made  crude  pottery. 

Erected  stone  monuments,  buried  the  dead. 

A  period  of  many  wars  and  migrations. 

4.  Age  of  Metals. 

•(a)  Copper  and  .gold  first  used  because  found  pure  in  nature; 
could  be  shaped  by  hammering  and  did  not  have  to  be 
melted. 

(b)  Bronze,  an  alloy  of  melted  copper  and  tin  which  made  ex- 

cellent implements  and  did  not  require  great  heat  to  melt. 

(c)  Iron,  required  skillful  smelting  and  tempering,  needing  much 

higher  temperature.     Best  metal  for  all  uses.     Brings 
us  down  to  modern  times. 


THE  DEVELOPMENT  OF  CIVILIZED  MAN 


337 


TABLE    I. 

^howing    Conditions    in    Europe    during  the   Development  of  Man 
Adapted    from   Osborn's  "Men  of  The  Old  Stone  Age" 

Time 

Cl  imafe 

dnirnals 

Implements 

Human  races 

Postglacial 
25.00O  years 

J 

Deer,      bison,    horse, 
chamois,     ibex 

Iron      /OOO  B.C 
Bronze   /OOO  yrs. 
Pottery 
Polisheaf  stone 
5000  yrs. 

Carving,  painting 

Clipped  flints 
25,000  yrs. 

Homo  sapiens 
Brain  capacity  eoOOcai 
Cro-magon  ffaco 
Brain  capacity  reaOccm 

4.  Glacial  Period 
25.000  years 

\ 

Reindeer,     arctic  far, 
muskox 

3.  Interglacial 
Period 

100.  000  years 

} 

Bison,      horse, 
hippopotamus, 
elephant,     lion, 
rhinoceros, 
sabre  -tooth  tiger. 

Neanderthal  Race 
Brain  capacity  I600ax 

j      - 

Rough  flints 
Z5.000  yrs. 

Piltdown   Race 
Brain  capacity  I400ca 

3  Glacial  Period 
25.000  years 

<^ 

Reindeer, 
wooly  mammoth 

\ 

Hippopotamus, 

rhinoceros  , 

2.  Inferglacial 
Period 

elephant, 
stag,     bison, 

' 

Heidelberg  Race 

200,000  years 

; 

horse 

2.G/ov/o/  Period 
25,  OOO  years 

Reindeer, 
wooly  mammoth. 

(  Interglaciat 
Period 
JS.OOOyears 

) 

Hippopotamus, 
elephant, 
rhinoceros. 

(Eoliths?) 

1.  Glacial  Period 
Z5.00O  years 

Mush  ox     in 
England. 

(Trinil  race  lived  in  Jowt 
Brain  capacity  9OOcfn 

FIG.  111.    From  Pearse. 

The  period  of  written  history  extends  back  at  most,  only  into 
the  bronze  age  so  we  can  see  how  comparatively  recent  has  been 
our  modern  development,  and  how  slow  was  man's  progress  in  his 
earlier  stages. 


338  BIOLOGY  FOR  BEGINNERS 

With  our  modern  civilization  has  come  a  complete  change  in  the 
manner  of  life.  While  we  would  not  relish  going  back  to  the  life 
of  the  cave  dweller,  still  we  pay  a  penalty  for  our  safer  and  easier 
methods  of  living.  Primitive  man,  if  he  survived  at  all,  was  neces- 
sarily a  hardy,  outdoor  animal,  eating  hard  foods,  having  a  sturdy 
and  little  protected  body,  and  literally  "  earning  his  bread  by  the 
sweat  of  his  brow."  Now  we  have  so  learned  to  control  our  en- 
vironment that  we  live  quiet,  safe,  indoor  lives,  protect  our  tender 
bodies  with  houses  and  clothes,  and  provide  ourselves  with  .soft 


FIG.  112.  At  right,  a  carved  flint  from  Denmark, 
of  the  Old  Stone  Age;  at  left,  a  polished  stone  axe 
head  from  Ireland,  of  the  New  Stone  Age.  From 
Kellogg. 

and  delicate  cooked  foods.  On  the  other  hand  we  have  developed 
our  brain  and  nervous  system  so  that  it  has  to  take  over  the  work 
previously  done  by  muscle  and  brawn.  Hence  we  are  overworking 
our  latest  acquisition,  our  intelligence,  at  the  expense  of  our 
bodies. 

Is  it  any  wonder  then  that  we  now  have  fat  and  flabby  muscles, 
weak  lungs,  delicate  skin,  and  degenerate  teeth,  combined  with 
overworked  nerves?  If  we  are  to  develop  to  its  highest  efficiency 
the  wonderful  mind  which  the  Creator  has  given  us,  we  have  to 


THE  DEVELOPMENT  OF  CIVILIZED   MAN  339 

make  special  effort  to  keep  our  bodies  strong,  even  though  physical 
strength  is  no  longer  the  one  essential  in  the  struggle  for 
existence. 

,To  this  end  modern  civilization  is  attempting,  by  healthful 
living  conditions,  by  education  in  biology  and  hygiene,  and  by 
systematic  exercise,  to  maintain  as  healthy  a  body  as  that  of  our 
ancestor  with  the  stone  hatchet,  combined  with  all  the  marvelous 
abilities  and  achievements  of  the  civilized  mind. 

We  do  not  have  to  depend  wholly  upon  the  evidence  of  human 
remains  to  get  an  idea  of  how  our  ancient  ancestors  lived.  Some 
Australian  and  African  races  are  still  almost  in  the  stage  of  primi- 
tive man.  Some  central  African  tribes  have  no  houses  but  sleep  hi 
what  are  practically  nests;  they  hunt  with  stone  clubs,  do  not  know 
the  use  of  even  the  bow  and  arrow,  cultivate  no  crops,  and  eat 
human  flesh.  Certain  natives  of  Patagonia  are  still  living  in  the 
Stone  Age  so  far  as  their  culture  is  concerned.  New  Caledonia  fur- 
nishes examples  of  man  but  little  further  advanced,  and  some  tribes 
of  Ceylon  and  Australia  are  living  in  even  more  primitive  stages  of 
development.  Still,  low  as  this  culture  may  be,  it  is  yet  wholly 
unapproached  or  resembled  by  the  life  of  the  lower  animals. 

Anthropologists  classify  the  human  species  in  different  ways, 
but  are  generally  agreed  upon  four,  or  perhaps  five  races,  distin- 
guished about  as  in  the  following  table: 


340 


BIOLOGY   FOR  BEGINNERS 


Lowest 
Langua 
Rapidl 


i 

Is 

O    cj 

G    C 

II 

.£?* 


i.al  < 

ll|   I 

&<K    o 


§•  - 

I    I 

w     ° 

111 

III 
p^l 


THE  DEVELOPMENT  OF   CIVILIZED   MAN  341 

COLLATERAL   READING 

Primer  of  Evolution,  Clodd,  Chap.  XI:  Story  of  Primitive  Man,  Clodd, 
entire;  Story  of  Creation,  Clodd,  entire;  Whence  and  Whither  of  Man, 
Tyler,  pp.  211-308;  Winners  in  Life's  Race,  Buckley,  pp.  333-353;  Animal 
Life,  Thompson,  pp.  320-350;  Man  Before  Metals,  Joly,  entire;  Anthro- 
pology, Tyler,  entire;  The  Next  Generation,  Jewett,  pp.  153-161. 


SUMMARY 

1.  Records  of  ancient  man  from 

Written  history. 
Monuments  and  inscriptions. 
Stone  implements  and  remains. 
Human  bones. 

2.  Characteristics  of  primitive  man. 

Brain  larger  than  other  animals. 
Bram  smaller  than  present  man. 
Low  forehead  and  sloping  brow. 
Heavy  jaw  and  receding  chin. 

3.  Stages  of  development  in  occupation. 

Primitive  man  without  weapons  or  fire. 
Hunter,  using  spear,  bow  and  arrow,  able  to  control  fire. 
Herdsman,  wandering  for  food  supplies,  domestication  of  animals. 
Cultivator  of  the  soil,  permanent  home,  crops  stored  for  future. 

4.  Stages  of  development  in  implements  used. 

Primitive  man  without  implements. 
Old  Stone  Age. 
New  Stone  Age. 
Age  of  Metals 

Copper. 

Bronze. 

Iron. 

5.  Results  of  present  higher  mental  development. 

Body  less  strong  and  hardy. 

Brain  greatly  developed  and  may  be  overworked. 

6.  Races  of  modern  man. 

(See  tabulation  in  text.) 


CHAPTER  XXXVH 
FOOD 

Vocabulary 

Assimilated,  made  like  and  built  into  tissut. 

Calorie,  the  amount  of  heat  used  to  raise  a  pound  of  water  4  deg.  F. 

Ratio,  proportion. 

Lipoid,  a  tissue  building  substance,  somewhat  like  fats. 

Vitamines,  active  substances  in  some  foods,  necessary  to  health. 

All  living  things  are  alive  because  energy  is  liberated  within 
them.  This  energy  depends  upon  oxidation  and  oxidation  involves 
the  union  of  oxygen  with  the  living  tissue.  This  process  destroys 
the  substances  oxidized,  leaving  behind  waste  products,  carbon 
dioxide,  water,  and  nitrogenous  compounds,  and  necessitating 
the  replacement  of  the  oxidized  tissue.  .  Replacement  of  tissue 
means  the  taking  in  of  food,  which  is  a  vital  necessity  to  all  living 
organisms. 

If  food  is  assimilated  faster  than  it  is  used,  growth,  or  storage 
of  excess,  results.  In  plants  little  energy  is  liberated  and  growth 
may  be  continuous;  in  animals  a  point  is  reached  where  oxidation 
balances  assimilation  and  growth  practically  ceases. 

Definition.  Food  may  be  denned  as  any  substance  which,  when 
taken  into  a  living  organism,  produces  energy  or  builds  tissue. 
The  energy  is  necessary  for  any  life,  the  tissue  building  may  be  to 
repair  used  organs  or  for  increase  in  growth. 

The  chemical  composition  of  all  living  things  is  much  the  same. 
They  are  composed  of  a  small  number  of  elements  and  all  depend 
upon  the  vitality  of  protoplasm  for  their  life.  (See  ch.  3,  4,  5.) 

Naturally  the  foods  that  produce  these  living  tissues  are  also 
similar  in  composition,  though  numerous  in  kind.  The  general 
classes  of  food  stuffs  (nutrients)  have  been  discussed  in  Chapter  4, 

342 


FOOD  343 

where  their  composition  and  properties  are  tabulated,  and  grouped 
as  inorganic  and  organic  matter.  Here  we  shall  take  up  their 
functions  in  relation  to  the  life  and  growth  of  animals,  especially 
as  food  for  man. 

Functions  of  Inorganic  Foods.  Water  constitutes  about  sixty 
per  cent  of  all  animal  tissue,  usually  more  than  that  in  plants.  It 
is  a  necessity  to  plants  in  starch  making  and  in  both  plants  and 
animals  as  a  transporter  and  solvent  for  other  foods.  Though  not 
oxidized  in  the  body  it  is  a  very  essential  part  of  all  foods. 

Mineral  salts  compose  about  five  per  cent  of  all  animal  tissue. 
They  are  essential  in  formation  of  bone,  teeth,  blood,  digestive 
fluids,  and  are  used  to  supply  nitrogen,  sulphur,  phosphorus, 
and  iron  for  making  protoplasm.  Table  salt,  sulphate  and  phos- 
phate of  lime,  and  various  nitrates  are  important  examples. 

Functions  of  Organic  Foods.  Proteids  are  the  only  food  stuffs 
containing  nitrogen,  and  are  therefore  absolutely  essential  in  pro- 
duction of  living  tissue.  They  include  some  of  man's  most  valuable 
foods,  such  as  lean  meat,  white  of  eggs,  cheese,  gluten  in  wheat, 
legumin  in  peas  and  beans,  etc.  Proteid  matter  constitutes  about 
eighteen  per  cent  of  the  weight  of  man's  body.  The  chief  function 
of  proteid  foods  is  to  build  tissue.  They  build  anew  and  repair 
muscle  and  tendon,  bone,  cartilage,  and  skin  and  also  compose 
the  corpuscles  of  the  blood.  Proteids  may  also  be  oxidized  directly 
and  thus  may  be  used  to  furnish  energy.  While  this  actually 
takes  place  to  some  extent,  it  would  be  an  expensive  source  of  fuel 
and  it  would  also  put  too  great  a  strain  upon  the  digestive  and 
excretory  organs  if  all  energy  were  sought  from  this  class  of  foods. 

The  fats  and  carbohydrates  are  the  chief  energy  producers.  The 
former  occur  in  fat  meats,  butter,  fish,  and  eggs  among  animal 
foods,  and  in  olive  and  cotton  seed  oils,  nuts,  corn,  and  cocoa  from 
the  vegetable  world.  The  amount  of  fat  needed  varies  with  age, 
occupation,  and  other  conditions  but  if  more  is  taken  than  is  re- 
quired, it  may  be  stored,  almost  unchanged,  to  be  drawn  upon  if 
the  energy  supply  becomes  short.  About  fifteen  per  cent  of  the 
human  body  is  fat  tissue  and  much  of  our  energy  is  derived  from 
other  amounts  that  are  oxidized  directly. 


344  BIOLOGY  FOR  BEGINNERS 

Carbohydrates  (starches,  sugars,  and  cellulose)  comprise  the  bulk 
of  man's  nourishment.  They  are  found  in  all  vegetable  foods, 
grains,  potatoes,  fruits,  and  nuts.  Milk  furnishes  an  important 
animal  sugar.  Though  occupying  so  large  a  place  in  our  menu, 
carbohydrates  compose  hardly  one  per  cent  of  the  body's  weight. 
This  is  because  they  are  easily  oxidized,  furnishing  much  heat  and 
energy  and  if  any  excess  is  taken,  it  is  changed  into  fat  and  stored 
as  such. 

Thus  it  is  seen  that  while  proteid,  fat,  or  carbohydrates  may 
all  supply  energy,  neither  of  the  latter  can  perform  the  proteid's 
function  in  growth  and  repair  of  tissues.  However,  the  fats  and 
carbohydrates  serve  to  protect  the  valuable  proteids  by  being  first 
oxidized  and  saving  the  proteids  for  tissue  building  which  they 
alone  can  perform.  (See  "  Summary  of  Nutrients  "  at  end  of 
chapter.) 

Measurement  of  Food  Values.  There  is  no  way  of  measuring 
the  tissue-building  value  of  foods.  But,  since  all  may  produce  heat 
and  energy,  they  may  easily  be  measured  and  their  value  as  food 
computed  in  terms  of  heat  produced.  The  unit  of  measurement  is 
the  "  calorie  "  which  is  the  amount  of  heat  required  to  raise  the 
temperature  of  one  pound  of  water  four  (4)  degrees  Fahrenheit. 
Very  careful  experiments  have  shown  that  a  man  in  an  average 
day's  work  requires  food  enough  to  produce  2800  calories  of  energy. 

The  amount  of  energy  (number  of  calories)  required  varies  with 
age  and  occupation  as  shown  in  this  table. 

TABLE  I 
DAILY  CALORIE  NEEDS  (APPROXIMATELY) 

1.  For  child  under  2  years 900  calories 

2.  For  child  from  2-5  years 1200  calories 

3.  For  child  from  6-9  years 1500  calories 

4.  For  child  from  10-12  years 1800  calories 

5.  Fof  child  from  12-14  (woman,  light  work,  also) 2100  calories 

6.  For  boy  (12-14),  girl  (15-16),  man  sedentary 2400  calories 

7.  For  boy  (15-16),  (man  light  muscular  work) 2700  calories 

8.  For  man,  moderately  active  muscular  work 3000  calories 

9.  For  farmer  (busy  season) 3200  to  4000  calories 

10.  For  ditchers,  excavators  etc 4000  to  5000  calories 

11.  For  lumbermen,  etc 5000  and  more  calories 


FOOD  345 

The  energy  required  for  various  degrees  of  exercise  are  shown 
below  and  one  can  compute  the  number  of  calories  used  per  day 
by  multiplying  the  calories  per  hour  by  the  hours  of  each  kind  of 
exercise  per  day.  Do  this  and  see  how  near  it  comes  to  the  esti- 
mate for  a  person  of  your  age  in  Table  I. 

TABLE  II 
AVERAGE   NORMAL  OUTPUT  OF  HEAT  FROM  THE  BODY 

Average 
Conditions  of  Muscular  Activity  Calories 

per  Hour 

Man  at  rest,  sleeping 65  calories 

Man  at  rest,  awake,  sitting  up 100  calories 

Man  at  light  muscular  exercise 170  calories 

Man  at  moderately  active  muscular  exercise 290  calories 

Man  at  severe  muscular  exercise 450  calories 

Man  at  very  severe  muscular  exercise 600  calories 

Food  Proportions.  In  order  that  the  body  may  have  tissue 
building  foods  and  fuel  foods  in  healthful  proportions,  we  ought 
to  eat  from  two  to  three  ounces  of  proteid  per  day,  and  enough 
fats  and  carbohydrates  to  make  up  the  number  of  calories  which 
we  may  require  as  indicated  above. 

Since  the  fuel  value  of  carbohydrates  is  only  |  to  J  that  of  fats, 
our  diet  should  have  two  or  three  times  as  much  carbohydrate, 
especially  in  warm  weather,  when  the  concentrated  fuel  of  the  fats 
is  less  needed.  Still  another  way  of  reaching  the  same  result  is 
to  take  sV  ounce  of  proteid  for  each  pound  of  our  weight,  and  enough 
of  the  fuel  foods  (fats  and  carbohydrates)  to  make  up  the  re- 
quired number  of  calories,  for  energy  production.  This  makes  a 
diet  rather  low  in  proteid  especially  for  growing  children,  but  our 
usual  mistake  is  to  use  too  much,  rather  than  too  little  proteid, 
and  one  good  authority  sets  the  amounts  even  lower. 

A  safe  proportion  for  growing  boys  and  girls  would  be  about 
2  or  2J  ounces  of  proteid  per  day,  and  enough  fuel  foods  to  supply 
the  required  energy,  which  will  depend  upon  the  age  and  activity 
as  already  stated. 


346  BIOLOGY  FOR  BEGINNERS 

The  carbohydrates  ought  always  to  be  more  abundant  than 
the  fats,  because  of  the  much  greater  amount  of  energy  produced 
by  the  latter.  This  is  especially  true  in  warm  weather,  when  the 
proportion  of  four  times  as  much  carbohydrates  will  be  about  the 
proper  diet. 

If  the  above  proportions  are  followed  for  all  three  food  stuffs, 
the  ratio  for  all  will  be  about,  — 

Proteid,  one;  fat,  one;   carbohydrate,  four. 

Need  of  Mixed  Diet.  We  require  proteids,  fats,  and  carbohy- 
drates in  about  the  proportions  1:1:4  but  there  is  no  one  food 
that  contains  these  nutrients  in  these  proportions,  so  it  is  evident 
that  a  mixed  diet  is  necessary.  When  foods  are  properly  selected, 
so  that  the  above  proportion  is  obtained,  we  have  what  is  known 
as  a  "  balanced  ration  "  and  this  should  be  the  aim,  both  of  those 
who  prepare  and  those  who  eat  foods. 

If  we  use  a  diet  largely  of  lean  meat,  we  have  too  high  a  per  cent 
of  proteid.  This  excess  is  thrown  off  by  the  kidneys  and  intestines 
as  waste.  It  overtaxes  these  organs  seriously  and  is  an  expensive 
and  unnecessary  form  of  diet.  In  the  same  way  an  excess  of  fat 
much  above  the  given  proportion,  such  as  would  come  from  a  diet 
rich  in  fat  meats  and  butter,  merely  wastes  the  extra  energy  or 
stores  it  as  unnecessary  fat  tissue  in  the  body. 

A  strict  vegetarian  diet  is  almost  sure  to  be  too  rich  in  carbo- 
hydrates and  has  the  same  result  as  do  fats,  fuel  is  wasted,  too 
little  tissue  material  is  provided,  and  fat  tissue  may  also  accumulate 
from  the  starches  being  transformed  and  stored  in  this  form. 

Remember  that,  in  general,  most  of  the  energy  should  come  from 
carbohydrates  and  fats,  and  only  enough  proteid  be  taken,  to  pro- 
vide for  tissue  building  and  repair.  If  our  diet  proves  to  be  high 
in  proteid,  we  are  burning  tissue  foods  for  fuel,  as  well  as  putting 
extra  strain  on  our  system,  to  remove  the  nitrogenous  waste  left 
by  proteid  oxidation. 

In  general,  man  has  learned  to  combine  foods,  to  correspond, 
roughly,  to  these  needs  as  will  appear  if  we  look  up  the  composi- 
tion of  familiar  combinations,  like  the  following, — 

"Meat  and, potatoes,"  " Bread  and  butter,"  " Bread  and  milk," 


FOOD  347 

"  Bread  and  cheese,"  "  Pork  and  beans,"  "  Potato  and  gravy," 
"  Cereal  and  cream,"  "  Ham  sandwich." 

A  study  of  the  following  table  will  show  the  number  of  ounces 
of  proteid,  and  the  fuel  or  energy  values,  of  some  of  our  common 
foods.  The  amounts  of  each  food  stuff  taken  are  about  the  usual 
portion  or  "helping"  which  one  would  receive  at  table,  so  we  can 
calculate  how  much  proteid  and  energy  our  present  diet  provides, 
and  see  if  it  corresponds  to  the  amounts  mentioned  as  suitable  for 
our  age  and  occupation. 

From  this  table,  also,  it  is  possible  to  determine  whether  one's 
diet  has  the  proper  proportion  of  fat  and  carbohydrate,  in  pro- 
portion to  the  proteid,  if  one  is  using  the  1:1:4  ratio  as  a  basis. 

These  tables  are  used  through  the  courtesy  of  Professor  Frank  H. 
Rexford,  from  whose  "One  Portion  Food  Tables  "  they  are  taken. 
They  furnish  the  easiest  means  of  estimating  whether  one's  diet  is 
properly  balanced. 

Digestibility  of  Foods.  Not  only  must  the  nutrients  in  our  foods 
be  present  in  the  proper  proportions,  but  they  must  be  in  a  digesti- 
ble form,  or  else  they  are  wasted.  Careful  study  shows  that  vege- 
table proteids  and  fats  are  not  so  easily  digested  as  those  from 
animal  foods,  though  they  seem  to  be  cheaper. 

This  means  that  we  must  either  use  considerable  animal  food,  or 
else  increase  the  apparent  amount  of  vegetable  proteids  and  fats 
beyond  the  proportion  suggested  in  the  tables,  because  the  body 
does  not  so  readily  digest  them.  This  fact  balances  their  cheaper 
cost  to  a  great  extent,  and  is  also  evidence  that  man  is  intended  for 
a  mixed  diet,  obtaining  much  fat  and  proteid  from  animal  sources, 
and  his  carbohydrate  foods  from  the  plants. 

Cost  of  Foods.  Not  only  must  our  diet  be  selected  with  reference 
to  proper  amounts  of  the  nutrients  and  ease  of  digestibility,  but 
also  with  regard  to  the  cost  in  money.  This  is  affected  by  three 
things,  the  actual  price  of  the  food,  the  amount  of  water  and  waste, 
and  the  expense  of  preparation.  It  is  more  and  more  important  that 
we  shall  be  informed  as  to  the  composition  and  cost  of  foods,  and  for 
this  purpose  the  Government  has  published  many  bulletins,  which 
can  be  had  free  of  cost,  by  application  to  the  Department  of 


348 


BIOLOGY  FOR  BEGINNERS 


FOODS  PRIMARILY  OF  PLANT  ORIGIN 


FOOD  AS  WE  EAT  IT 

OF  THIS  THE  BODY  CAN 
USE 

This  Portion  can  Yield 
to  the  Body  in  Energy 
and  Heat  Units 

Muscle 
Builder 

For  Heat  and 
Energy 

Proteid 

Fat 

Carbo- 
hydrates 
(Starch 
and 
Sugar) 

Beverages 
Cocoa  

Ounces 
.11 
.01 

.19 
.16 
.18 
.18 
.19 
.22 
.11 
.1 
.06 

.14 
.13 
.12 
.12 
.12 
.09 

.07 
.13 
.04 
.11 
.21 

.02 
.05 
.01 
.04 

Ounces 
.33 
,17 

.27 
.09 
.04 
.03 
.08 
.48 
.13 
.09 
.008 

.2 
.16 
.37 
.18 
.22 
.16 

.003 
.02 

.001 
.03 

.02 
.02 
.37 
.01 

Ounces 
.19 

.27 

1.05 
.93 
1.04 
1.07 
1.2 
1.18 
.69 
.73 
.3 

1.6 
1.32 
.93 
1.3 
1.28 
.9 

.59 
.49 
.4 
.96 
1.56 

.78 
.77 
.15 
.58 

Calories 
123 
53 

216.3 
150.6 
151.3 
153.1 
182.08 
275 
125.3 
120.3 
44.4 

256.8 
209 
218.8 
211.9 
220 
168.3 

77.6 
76.5 
50.9 
124.72 
212.5 

98.5 
100.8 
116.3 

75 

Coffee  (cream  and  sugar  only) 

Bread 
Biscuit  soda 

Bread  corn 

"       graham  .  .           

"       wheat 

"      plain  rolls 

"       and  butter  . 

Crackers  saltines  

"        soda  

Toast  dry 

Cake 
Chocolate  layer 

Cookies  molasses 

Doughnuts         .                

Frosted                          

Fruit  

Soonsro 

Cereals 
Corn  flakes                         

Oatmeal            ...       

Puffed  rice  

Rice  

Shredded  wheat  (2)  

Fruit 
Apple  baked  

Bananas                                 

Olives  green       

Oranges 

FOOD 


349 


FOODS  PRIMARILY  OF  PLANT  ORIGIN.  —  Continued 


FOOD  AS  WE  EAT  IT 

OF  THIS  THE  BODY  CAN 

USE 

This  Portion  can  Yield 
to  the  Body  in  Energy 
and  Heat  Units 

Muscle 
Builder 

For  Heat  and 
Energy 

Proteid 

Fat 

Carbo- 
hydrates 
(Starch 
and 
Sugar) 

Miscellaneous 
Brown  gravy  

Ounces 
.03 
.26 
.36 

.05 
.08 
.13 

.29 
.14 
.65 
.15 

.1 
.16 
.12 
.11 

.26 
.04 
.09 
.06 

.38 
.11 
.1 
.09 
.13 
.13 

Ounces 
.26 
.27 
.02 
.74 

.14 
.32 
.19 

.31 
.4 
.42 
.15 

.3 
.16 
.28 
.1 

.25 
.02 
.22 
.16 

.07 
.34 

.04 
.12 

Ounces 
.07 
.32 
2.00 
.02 

.04 
.08 
.12 

1.44 
1.4 
1.51 
1. 

.49 

.35 
.55 
.92 

.02 
.52 
.29 
.15 

1 
.17 
.02 
.33 
.33 
.02 

Calories 
81.2 
114.3 
286.2 
100.4 

47.8 
103.4 
80.1 

282.8 
297.2 
362 
177 

148.8 
102.4 
149.5 
146.3 

100.1 
70.4 
102.1 
67.6 

182.8 
124.8 
16 
60 
91.2 
192.8 

Hash  beef 

Macaroni  .  .  . 

Salad  dressing  (French) 

Nuts 
Almonds  

English  walnuts  .  .    . 

Peanuts 

Pie 
Apple  
Lemon 

Mince        .... 

Pumpkin  ...                            ... 

Pudding 
Blanc  mange  (chocolate)  

Custard  

Rice 

Tapioca  .  .           .        

Salad 
Egg  mayonnaise  

Fruit 

Potato  
Tomato  (with  mayonnaise)  

Soup 
Bean 

Cream  of  celery  
Consomme  

Clam  chowder  
Tomato  
Vegetable  (canned)  

350 


BIOLOGY  FOR  BEGINNERS 


FOODS  PRIMARILY  OF  PLANT  ORIGIN  —  Continued 


f 

FOOD  AS  WE  EAT  IT 

OF  THIS  THE  BODY  CAN 
USE 

This  Portion  can  Yield 
to  the  Body  in  Energy 
and  Heat  Units 

Muscle 
Builder 

For  Heat  and 
Energy 

Proteid 

Fat 

Carbo- 
hydrates 
(Starch 
and 
Sugar) 

Sugars 
Candy  chocolate  .       

Ounces 
.01 
.06 

.31 
.22 
.69 
.05 
.03 
.01 
.08 
.04 
.01 
.04 
.09 
.09 
.09 
.1 
.11 
.04 
.08 

Oun  es 
.01 
.15 

.18 
.65 
.61 
.002 
.09 
.003 
.03 
.02 

.15 
.09 
.06 
.26 
.01 
.03 
.04 

Ounces 
.73 
.95 
.89 

.25 

1.08 
.6 
.21 
.15 
.16 
.04 
.52 
.35 
.03 
.15 
.54 
1.26 
.68 
.26 
.56 
.18 
.08 

Calories 
90 
160 
103.9 

27 

182 
97.5 
48.72 
26.1 
35.2 
5.5 
74.25 
49.2 
7 
65.7 
66.6 
173.4 
100.4 
98.1 
78 
26.8 
16.4 

Chocolate  almonds  

]V£aple  syrup  

Sugar  (granulated  or  loaf)  
Vegetables 
Beans  baked      

"      kidney 

"      strinsr 

Beets                                

Cabbage  boiled  

Celery      

Corn  canned        .  .             

Carrots            

Lettuce     

Onions  creamed      

Potatoes  sweet 

"        white  mashed  

"            "      baked  

Succotash           

Tomatoes  sliced 

"          stewed          .  . 

Agriculture  at  Washington.    Lists  of  all  publications  will  be  sent 
on  application. 

While  we  cannot  devote  enough  space  to  the  topic  to  compare 
the  different  kinds  of  food,  their  cost  and  composition,  and  methods 
of  preparation,  even  a  slight  study  of  your  own  diet,  in  the  light  of 
this  chapter,  will  show  two  facts:  first,  Americans  eat  more  food 


FOOD 

FOODS  PRIMARILY  OF  ANIMAL  ORIGIN 


351 


FOOD  AS  WE  EAT  IT 

OF  THIS  THE  BODY  CAN 

USE 

""C     ^% 

£  S  £ 

831 

•It! 

!«-o 

£H    <u    a 
.2  "5  ^ 

§2 

Muscle 
Builder 

For  Heat  and 
Energy 

Proteid 

Fat 

Carbo- 
hydrates 
(Starch 
and 

Sugar) 

Beef 
Corned        

Ounces 
.21 
.26 
.43 

.37 

.05 
.26 
.05 
.19 

.49 

.48 
.24 

.32 
.56 
.44 

.62 
.26 

.43 
.67 

.62 

Ounces 
!52 
.07 
.29 
.36 

.43 
.34 
.1 
.24 
.4 

.45 

.88 
.17 

.02 
.16 
.24 

.4 
.26 

.59 
.44 

.51 

Ounces 

.02 
.91 
.3 

.03 
.03 

.08 

Calories 
174.2 
49.4 
125.2 
137.1 

112.5 

122.4 
134.7 
123.6 
110.2 

179.1 
296 

78.5 

101  6 
105.9 
114.1 

187 
104 

210 
194.3 

108 

Dried  

Round  

Sirloin 

Dairy  Products 
Butter  
Cheese  full  cream 

Ice  cream  

Milk  whole 

Oleomargarine 

Eggs 
Boiled  (2)  :    . 

Omelet  

Scrambled 

Fish 
Cod    

Halibut  steak 

Salmon  canned      .  . 

Fowl 
Chicken  (fricasseed)  

Turkey  

Lamb 
Chops  (broiled)    .... 

Leg.  . 

Mutton 
Leg. 

352  BIOLOGY  FOR  BEGINNERS 

FOODS  PRIMARILY  OP  ANIMAL  ORIGIN  —  Continued 


FOOD  AS  WE  EAT  IT 

OF  THIS  THE  BODY  CAN 
USE 

This  Portion  can  Yield 
to  the  Body  in  Energy 
and  Heat  Units 

Muscle 
Builder 

For  Heat  and 

Energy 

Proteid 

Fat 

Carbo- 
hydrates 
(Starch 
and 
Sugar) 

Pork 
Bacon  

Ounces 
.1 
.47 
.49 

.41 
.4 
.33 

.56 

.24 

.32 
.21 

.7 
.65 
.56 

Ounces 
.66 
.95 

.55 

.49 
.37 
.48 

.8 

.02 
.04 
.04 

.26 
.1 
.17 

Ounces 

1.2 
1.19 
1.19 

Calories 
188.6 
309 
203.2 

314.2 
279.7 
302.7 

278.1 

32.2 
47.6 
36.4 

152 
104 
107.1 

Chops  

Ham  lean 

Sandwiches 
Cheese  

Eee 

Ham   . 

Sausages 
Country 

Shellfish 
Clams  

Lobster 

Oysters  

Veal 
Cutlets   ... 

Leg 

Liver 

than  is  required  and  second,  they  have  an  idea  that  the  most 
expensive  foods  are  the  most  nutritious. 

These  are  serious  mistakes,  overtaxing  both  the  digestive  system 
and  the  pocket  book,  and  no  subject  of  our  study  is  more  important 
than  the  one  giving  us  a  clear  idea  of  food  values  and  selection. 

Right  and  Wrong  Diets.  We  are  all  too  apt  to  let  our  artificial 
"  tastes  "  and  the  demands  of  fashionable  customs  over-rule  our 


FOOD  353 

natural  instincts  and  better  judgment  in  the  selection  of  foods. 
Costly,  highly-seasoned,  stimulating,  and  unnatural  substances 
are  frequent  invaders  of  our  digestive  apparatus,  to  the  detriment 
both  of  our  bodies  and  our  bank  accounts.  For  the  majority  of 
people  in  normal  health,  meats,  fish,  eggs,  milk,  butter,  cheese, 
sugar,  flour,  meal,  potatoes,  and  other  vegetables  make  a  fitting 
and  sufficiently  varied  diet  —  the  main  point  being  to  use  them  in 
proportions  suited  to  the  actual  needs  of  the  body  and  not  according 
to  acquired  whims  of  the  "  appetite." 

Another  fact  that  is  often  misunderstood,  even  after  a  study  of 
nutrients,  is  the  very  essential  nature  of  mineral  salts,  especially 


From  the  American  Museum  of  Natural  History. 

FIG.  113.  A  U.S.  soldier  in  the  field  is  allowed  a  daily  ration 
supplying  4199  calories  of  energy.  A  typical  daily  field  ration  supply- 
ing this  amount  of  energy  is  shown  above. 

iron,  calcium,  and  potash  compounds,  which  we  obtain  from  green 
vegetables,  otherwise  not  rich  in  food  value.  As  shown  by  the 
"Summary  of  Nutrients"  on  p.  357,  these  mineral* compounds  are 
a  necessary,  though  small  part  of  every  properly  balanced  diet. 
Furthermore,  the  fact  that  many  foods,  especially  of  vegetable 
origin,  contain  considerable  indigestible  matter  such  as  cellulose, 
or  connective  tissue,  is  also  of  value  as  supplying  a  certain  bulk  of 
matter  required  to  keep  the  digestive  apparatus  properly  filled  and 
active. 

A  diet  could  be  divised  made  up  of  highly  concentrated  and  pre- 
digested  foods,  which,  though  giving  all  necessary  nutrients,  would 
be  very  harmful,  because  of  relieving  the  digestive  organs  of  the 


354  BIOLOGY  FOR  BEGINNERS 

work  for  which  they  have  become  adapted,  and  without  which  they 
will  not  remain  in  health. 

Cooking.  Man  is  the  only  animal  which  has  learned  to  build  a 
fire,  hence  is  the  only  animal  to  use  cooked  food.  This  is  not  an 
unmixed  blessing,  for  our  digestive  apparatus  and  especially  our 
teeth  are  inherited  from  our  animal  ancestors,  and,  when  provided 
with  cooked  food,  are  relieved  of  work  for  which  they  were  adapted. 
This  leads  to  disuse  and  so  to  degeneration.  One  seldom  hears  of 
the  lower  animals  suffering  from  decayed  teeth  or  indigestion, 
both  of  which  are  almost  universal  in  man,  due  partly  to  too  abund- 
ant, too  delicately  prepared,  and  unnatural  foods. 

Cooking  of  food  performs  three  functions:  First,  it  changes  the 
mechanical  and  chemical  condition  so  as  to  make  it  more  easily 
digestible ;  second,  it  makes  food  more  appetizing  in  appearance  or 
flavor,  which  quickens  the  flow  of  digestive  fluids  and  actually  aids 
digestion;  third,  the  high  temperature  kills  any  dangerous  bac- 
teria, organisms,  or  parasites  that  the  food  may  contain.  This  is 
very  important. 

Cooking  meat  develops  its  pleasing  taste  and  odor,  softens  con- 
nective tissue,  and  makes  it  "  tender,"  though  too  high  temperature 
may  harden  the  proteids  of  the  lean  portions.  Beef  extracts  and 
thin  soups  are  very  agreeable  to  the  taste,  but  contain  very  little 
nourishment  since  the  meat  proteids  and  fats  are  not  soluble  in 
water.  These  broths  are  useful  as  appetizers  or  mild  stimulants 
but  are  of  slight  value  as  food. 

In  cooking  eggs,  especially  by  frying,  the  proteid  (albumen)  is 
hardened  and  made  less  digestible  than  in  the  raw  state.  Milk, 
also,  if  heated  to  boiling,  is  made  less  valuable  as  food;  though 
when  pasteurized  the  heat  is  regulated  so  as  to  kill  most  bacteria, 
but  not  to  reach  a  point  high  enough  to  impair  its  food  value. 
When  the  vegetable  foods  are  cooked  the  changes  are  chiefly  the 
softening  of  the  cellulose  and  the  breaking  of  the  insoluble  walls 
around  the  starch  grains,  thus  exposing  them  to  digestive  fluids 
and  partly  dissolving  the  starch  in  the  hot  water  or  steam. 

In  baking  all  flour  foods,  the  aim  is  to  make  the  material  "  light," 
and  porous  so  as  to  be  more  easily  broken  up  and  digested  in  the 


FOOD  355 

alimentary  canal.  This  lightness  may  be  secured  by  the  mere 
expansion  of  steam  in  the  dough,  but  it  is  usually  caused  by  use  of 
yeast  or  baking  powder,  which  produce  carbon  dioxide  within  the 
batter.  The  gluten  (proteid),  always  present  in  flour,  is  sticky 
enough  to  retain  the  gas,  which  expands  with  the  heat  of  cooking, 
filling  the  loaf  with  countless  bubbles  and  making  it  porous.  Finally 
the  heat  stiffens  the  gluten  and  starch  and  drives  out  much  of  the 
enclosed  gas  and  we  have  the  "  light,"  porous,  and  digestible  bread 
or  pastry,  instead  .of  an  indigestible  paste  of  uncooked  flour  and 
water. 

"  Special  Foods."  There  are  no  foods  for  special  organs.  Fish 
is  not  a  "  brain  food,"  nor  celery  a  "  nerve  food,"  nor  meat  a 
"  muscle  food."  The  savage  eats  the  heart  of  his  fallen  foe  to  ab- 
sorb his  courage,  but  we  ought  to  be  beyond  that  stage.  If  we  use 
a  properly  balanced  diet  our  cells  will  select  what  they  need  in 
proportion  as  we  use  them.  The  only  way  to  increase  the  brain 
power  is  to  use  the  brain,  —  not  by  eating  foods  rich  in  phosphorus 
because  the  brain  tissue  contains  this  element. 

If  eating  strong  muscle  made  us  strong,  we  ought  to  have  a  diet 
of  the  toughest  meat  possible.  However  the  only  way  to  persuade 
nature  to  give  us  more  strength,  is  by  using  what  we  have  and 
furnishing  her  a  proper  food  supply  to  select  from. 

To  be  sure,  if  phosphorous  compounds  are  lacking,  the  nerves 
will  suffer;  if  proteid  be  absent,  our  muscle  tissue  might  feel  the 
lack,  but  in  a  balanced  diet  this  is  never  the  case.  An  excess  of  any 
element,  above  what  is  normally  used  in  the  body,  does  not  develop 
any  special  part,  but  is  merely  wasted.  Extra  proteid  is  not  needed 
for  extra  work;  it  is  the  fuel  food  that  supplies  the  energy,  the 
proteid  requirement  being  almost  constant  for  all  grown  persons 
and  only  slightly  varying  for  younger  people. 

Lipoid.  A  shortage  of  fat  in  the  diet,  not  only  reduces  the  energy 
produced,  but  has  long  been  associated  with  a  lowering  of  nervous 
activity.  This  is  now  explained  by  the  discovery  of  a  substance 
called  lipoid,  in  the  cell  walls  of  the  body,  especially  in  the  outer 
layer  of  the  nerve  fibers  and  brain  cells. 

Lipoid  resembles  fat  in  many  ways,  but  contains  nitrogen  and 


356  BIOLOGY  FOR  BEGINNERS 

phosphorus  which  ordinary  fats  do  not.  It  is  affected  by  alochol, 
anaesthetics,  and  poisons  and  thus  may  be  the  means  by  which 
these  act  upon  the  system.  At  all  events  it  seems  to  be  derived 
from  fat  foods  and  is  very  essential  to  the  nervous  system. 

Vitamines.  It  has  been  found  that  a  diet  restricted  to  a  few 
foods,  especially  if  they  all  be  cooked,  does  not  always  result  in 
proper  nourishment,  even  though  the  balance  may  seem  to  be  cor- 
rect. This  has  led  to  the  belief  that  there  are  substances  called 
vitamines  in  certain  foods,  which  are  necessary  to  health  and  are 
destroyed  by  cooking.  In  order  to  supply  these,  the  diet  should 
include  a  moderate  amount  of  uncooked  foods,  such  as  fruits,  let- 
tuce, celery,  tomatoes,  milk,  and  butter. 

Fruits  and  vegetables  are  important  for  another  reason.  They 
produce  alkaline  substances  when  digested  and  these  neutralize 
harmful  acids  formed  by  the  digestion  of  proteids.  They  are  also 
our  chief  source  of  iron  and  some  other  necessary  mineral  salts, 
and  cannot  be  safely  omitted  from  the  dietary,  even  though  their 
calorie  value  is  not  always  very  high. 

If  energy  alone  was  all  that  is  required  of  food  we  could  get  our 
2500  calories  from  about  twenty  ounces  of  sugar  or  white  of  egg, 
or  half  that  amount  of  clear  butter.  Both  our  instinct  and  ex- 
perience teach  us  that  this  would  not  support  a  healthful 
life. 

Dietary  Diseases.  Certain  natives  of  Japan  and  the  Philippines 
live  largely  on  rice.  This  supplies  plenty  of  energy  but  lacks  other 
essential  nutrients  and  they  suffer  from  a  disease  called  beri-beri, 
which  is  quickly  cured  by  a  change  of  diet.  Pellagra  is  a  sickness 
which  occurs  in  our  southern  states,  and  seems  to  be  caused  by  a 
diet  poor  in  proteid.  Scurvy  is  another  dietary  disease,  caused  by 
lack  of  fresh  fruits  and  vegetables.  It  used  to  be  common  among 
sailors  whose  long  voyages  forced  them  to  live  on  salt  meats  with- 
out any  fresh  foods,  and  was  promptly  relieved  by  use  of  fruit  and 
fruit  juices  when  they  came  ashore.  Long  ago  the  sailing  vessels 
used  to  carry  casks  of  lime  juice  to  prevent  this,  and  now  it  has 
become  a  custom  to  refer  to  any  sailor  on  a  slow  sailing  vessel  as 
a  "  lime  juicer." 


FOOD 


357 


Experience  teaches  that 

1.  Food  must  be  sufficient  in  amount. 

2.  Diet  must  contain  proper  proportion  of  the  nutrients. 

3.  Diet  must  contain  vitamines. 

4.  Diet  must  include  a  considerable  variety  of  foods. 

SUMMARY  OF  NUTRIENTS 


Nutrients 

Composition 

Function 

Foods  containing 

Proteids 

C,H,0,  N,S,P, 

Build  tissue 

Lean  meats,  eggs, 

K,  Ca,  Cl,  Fe 

Protoplasm 

beans,  peas,  milk 

Some  energy 

Carbohydrates 

(C,  H2,  0) 

Energy 

Sugar,      cereals, 

Stored  as  fat 

bread,  corn  meal 

Some  tissue 

Fats  and  oils 

(C,  H)  O 

Energy 

Butter,  lard,  milk, 

Stored  as  fat 

cheese,  olive  oil, 

nuts 

Water 

H2O 

60%  tissue 

Taken  as  water  in 

Blood,  fluids 

all        vegetables 

Transporter 

fruits,  all  foods 

Mineral  Salts 

Phosphates 

H3P04 

Bone 

Grains          (whole) 

Protoplasm 

meats,  fish,  milk 

Aid  digestion 

Salt 

NaCl 

Essential  in  blood 

Taken    as    salt    in 

Appetizer 

almost  all  food 

Iron  compounds 

FeCO3 

Haemoglobin 

Spinach,       lettuce, 

Oxygen  carrier 

green      foods, 

prunes,    meats 

Potassium  com- 

K2S04 

Essential  in  blood 

Vegetables 

pounds 

Calcium      and 

Ca,  Mg 

Regulate  nerve  and 

Grains          (whole) 

magnesium 

heart  action 

Vegetables 

compounds 

NOTE.  —  Look  up  tests  for  as  many  of  the  above  as  you  can. 

NOTE.  —  There  are  many  kinds  of  proteids  as, 

(1)  Myosin  in  meats;    (2)  legumin  in  peas  and  beans;    (3)  casein  in 


358  BIOLOGY  FOR  BEGINNERS 

milk  and  cheese;    (4)  gluten  in  grains;    (5)  albumin  in  eggs;   but  all  con- 
tain nitrogen. 

There  are  many  kinds  of  carbohydrates  as, 

(1)  Several  kinds  of  starches  (corn,  potato,  sago,  arrow  root). 

(2)  Many  kinds  of  sugars  (cane,  saccharose:  — grape,  glucose:  — milk, 
lactose:  —  fruit,  fructose). 

(3)  Cellulose. 

(4)  Gums  and  resins  (some  of  them). 

THE  FUNDAMENTAL  PRINCIPLES  OF  CORRECT  EATING 

The  human  body  is  very  much  like  an  engine.  It  needs  fuel  to 
keep  it  running.  As  it  has  to  be  built  so  must  it  be  repaired  from 
time  to  time,  also  it  must  be  regulated,  hence,  we  need  A  —  Fuel 
food;  B  — Building  or  repair  food;  C  -^Regulating  food. 

Fuel  Foods.  As  in  the  case  of  an  engine,  the  main  requirement 
is  for  fuel.  Unlike  an  engine,  however,  if  the  human  body  does  not 
secure  sufficient  fuel  it  will  literally  burn  to  death,  the  tissues  being 
drawn  upon  to  supply  the  fuel.  On  the  other  hand,  the  human 
engine  may  easily  become  overstoked  by  an  excess  of  fuel.  The 
following  list  shows  the  main  fuel  foods,  the  great  foundation  foods 
of  the  diet,  that  supply  energy  for  muscular  work.  Mental  work 
requires  so  little  extra  fuel  that  it  is  not  necessary  to  consider  it 
specially.  There  are  three  groups  of  fuel  foods.  Here  they  are  in 
the  order  of  their  cost  per  calorie,  those  giving  most  energy  for 
the  money  heading  the  list. 

1.   Starchy  Foods 

Cornmeal  Rice  Split  peas,  yellow 

Hominy  Macaroni  Dried  navy  beans 

Broken  Rice  Spaghetti  Bread 

Oatmeal  Cornstarch  Potatoes 

Flour  Dried  lima  beans  Bananas 

2.   Sugars  3.  Fats 

Sugar  Candy  Drippings  Peanut  butter 

Corn  syrup        Molasses  Lard  Milk 

Dates  Most  Fruits          Salt  pork  Bacon 

Oleomargarine        Butter 
Nutmargarine         Cream 


FOOD  359 

About  85  per  cent  of  the  fuel  for  the  body  should  come  from  these 
groups,  using  starchy  foods  in  the  largest  amounts,  fats  next,  and 
sugar  least. 

Building  and  Repair  Foods.  These  are  divided  into  proteids  and 
mineral  salts. 

1.  Proteid,  or  "  Body  Bricks."    These  food  elements  are  found 
in  greatest  abundance  in  lean  meat  of  all  sorts  (including  fish,  shell 
food,  and  fowl),  milk,  cheese,  eggs,  peas  and  beans,  lentils,  and 
nuts.    There  is  also  a  fair  amount  of  proteid  in  cereals  and  bread 
(about  10  per  cent),  which  are  both  building  and  fuel  foods.    Most 
foods  contain  some  proteid.    Those  above-mentioned  are  richest 
in  proteid  and  hence  are  termed  "  Building  "  or  "  Repair  Foods." 

The  following  is  a  list  of  the  building  and  repair  foods  in  the  order 
of  their  cost,  those  giving  most  building  and  repair  material  for  the 
money  heading  the  list. 

Beans  (dried  white)  Bread,  whole  wheat  Macaroni  Eggs      (second 

Dried  peas  Bread,  graham          Mutton,  leg  grade) 

Oatmeal  Salt  cod  Beef,  lean  rump  Halibut 

Cornmeal  Milk,  skimmed          Milk  Porterhouse  steak 

Beans,  dried  lima      Cheese  (American)   Beef,  lean  round  Eggs  (first  grade) 
Bread  Peanuts  Lamb,  leg  Almonds,  shelled 

2.  Mineral  Salts.    These  are  found  in  milk,  green  vegetables, 
fruits,  and  cereals  made  from  the  whole  grains,  and  egg  yolks. 

Regulating  Foods.  1.  Mineral  Salts.  These  minerals  which 
have  been  mentioned  as  repair  foods,  are  also  regulating  foods 
and  help  to  keep  the  machinery  running  properly. 

2.  Water.     Water   is   an   important   regulating  food.     Many 
people  drink  too  little.    Six  glasses  of  water  a  day  is  the  average 
requirement  —  one  between  meals  and  one  at  meals. 

3.  Ballast  or  Bulk.    This  is  furnished  by  cereals  and  vegetable 
fiber,  which  is  found  in  whole  wheat  or  Graham  flour,  in  bran, 
leaves  and  skins  of  plants,  and  skins  and  pulp  of  fruits.  Examples 
are:     Vegetables  —  Lettuce,   Parsnips,   Carrots,   Turnips,   Celery, 
Oyster   Plant,    Cabbage,    Brussels    Sprouts,   Tomatoes,    Salsify, 
Spanish    Onions,    Spinach.       Fruit  —  Apples    (Baked    or    Raw), 


360  BIOLOGY  FOR  BEGINNERS 

Pears,  Currants,  Raspberries,  Cranberries,  Prunes,  Dates,  Figs, 
Oranges. 

4.  Hard  Foods.    Vigorous  use  of  teeth  and  jaws  is  insured  by 
hard  foods,  such  as  crusts,  hard  crackers,  toast,  Zwieback,  fibrous 
vegetables  and  fruits,  celery  and  nuts,  which  are  necessary   to 
keep  teeth  and  gums  in  a  healthy  condition. 

5.  Accessories   or   Vitamines.     These   are  minute  substances 
(vitamines  and  Jipoids)  present  in  a  very  small  quantity  in  a  number 
of  foods  and  apparently  necessary  to  keep  the  body  in  health.    That 
is,  the  absence  of  these  elements  seems  to  lead  to  poisoning  of  the 
body,  which  results  in  such  disturbances  as  scurvy,  beri-beri,  and 
other  so-called  "  deficiency  "  diseases.     Milk,  eggs,  whole  wheat, 
corn,  oatmeal,  potatoes  and  oranges,  skins  or  hulls  of  cereals,  fresh 
meat,  fresh  peas  and  beans  are  thought  to  contain  them.    It  seems 
necessary  to  include  the  leaves  of  plants  (green  vegetables)  when 
the  seeds  (cereals,  grain,  flour,  etc.)  are  used  as  food  if  the  diet  is 
to  be  complete  and  well  balanced.    Fruit  and  vegetable  acids  are 
regulating.   They  keep  the  blood  alkaline  and  prevent  constipation. 

COLLATERAL   READINGS 

Principles  of  Nutrition,  At  water,  entire;  Studies  in  Physiology,  Peabody, 
pp.  41-61;  Elements  of  Cookery,  Williams  and  Fisher,  pp.  136-142,  look 
through;  Chemistry  of  Common  Things,  Brownlee,  pp  242-265;  Food 
Materials,  Richards,  pp.  1-19;  Pure  Foods,  Oleson,  pp.  1-32;  Plants  and 
their  Uses,  Sargent,  look  through;  Source,  Chemistry  and  Use  of  Food, 
Bailey,  look  through;  World's  Commercial  Products,  Freeman,  see  index; 
Food  and  Dietetics,  Hutchinson,  see  index;  Practical  Hygiene,  Harrington 
and  Richardson,  see  i  ex;  Feeding  the  Family,  Rose,  entire;  Human 
Foods,  Snyder,  see  index;  Children's  Diet  in  Home  and  School,  Hogan,  see 
index;  Food  and  Dietetics,  Norton,  see  index;  The  Cost  of  Food,  Richards 
and  Norton,  entire;  Foods  and  their  Adulteration,  Wiley,  see  index;  Ele- 
mentary Biology,  Peabody  and  Hunt  (Pt.  II),  pp.  44-63;  Physiology, 
Experimental  and  Descriptive,  Colton,  pp.  167-193;  Textbook  in  General 
Physiology  and  Anatomy,  Eddy,  pp.  51-89;  Applied  Physiology,  Overton, 
pp.  51-66;  Human  Mechanism,  Hough  and  Sedgwick,  pp.  95-97;  The 
Human  Body  and  Health,  Davidson,  pp.  35-44;  The  Human  Body, 
Martin,  pp.  88-105;  General  Science,  Clark,  pp.  60-69;  Elementary  Physi- 
ology, Huxley,  pp.  250-252,  291-303;  High  School  Physiology,  Hewes, 
pp.  87-91;  Essentials  of  Biology,  Hunter,  pp.  330-350;  U.  S.  Department 
of  Agriculture,  Farm  Bulletins,  23,  34,  74,  85,  93,  128,  142,  182,  249,  256, 
295,  etc.;  Periodical,  "The  Forecast,"  Philadelphia. 


FOOD  361 

SUMMARY 
Necessity  of  food. 

Living  things  use  energy. 
Energy  is  released  from  food  by  oxidation. 
Oxidation  destroys  tissue. 
This  tissue  has  to  be  replaced  by  food. 

Excess  of  food  used  for  growth  or  storage.     (Compare  plant  and  animal.) 
Definition  of  food. 
Functions  of  food-stuffs. 

Inorganic.     Water   (60%).     Transportation,    solvent    (photosynthesis). 
Mineral  salts  (5%). 

Phosphates,  chlorides,  nitrates,  carbonates. 
(Compounds  of  N,  S,  P,  iron,  lime,  etc.) 
Used  in  bone,  teeth,  blood,  fluids,  digestion,  etc. 
Organic.     Proteids  (18%). 

Composed  of  C,  H,  O,  N,  S,  P,  etc. 
Essential  to  living  tissue,  protoplasm. 
Found  in  lean  meat,  eggs,  cheese,  wheat,  beans,  peas. 
Fats  (15%). 

Composed  of  C,  H,  O. 

Easily  oxidized,  produce  energy,  excess  stored. 

Found  in  fat  meat,  butter,  eggs,  fish,  lard,  cotton  and  olive  oil,  corn, 

cocoa,  etc. 

Carbohydrates  (little  in  tissues). 
Composed  of  C,  H2,  O. 
Produce  energy  or  stored  as  fat. 
Found  as  sugar  in  cane,  fruits,  beets,  milk. 
Found  as  starch  in  vegetables,  grains,  nuts,  etc. 
Found  as  cellulose  in  most  vegetable  foods. 
Measurement  of  food  values. 

Energy  value  measured  in  "calories." 
About  2800  calories  needed  by  average  individual. 
Needs  vary  with  age  and  occupation. 
Food  proportions. 

Proteids  from  2  to  3  ounces  per  day. 

Fuel  foods  to  make  up  remaining  number  of  calories, 

,  ,_  .      ,  c          (  fats,  one  part, 
obtained  from  |  carbohydrates?  two  to  four  parts. 

Less  fats  in  warm  weather. 

Ratio  about,  proteid  :  fat  :  carbohydrates 

(1)     :(1):  (4) 

Balanced  Ration. 

No  one  food  has  nutrients  in  correct  ratio. 

Hence  a  mixed  diet  is  necessary. 

Animal  food  would  be  too  high  in  fat  and  proteid. 

Vegetable  food  would  be  too  high  in  carbohydrates. 

Excess  of  proteid,  a  dangerous  and  expensive  source  of  energy. 


362  BIOLOGY  FOR  BEGINNERS 

Digestibility  of  Foods. 

Vegetable  fats  and  proteids  less  digestible  than  animal. 
Value  of  both  vegetable  and  animal  foods. 

Cost  of  Food. 

Depends  on  price,  waste,  cost  of  preparation 
Expense  due  to  poor  selection. 

bad  preparation  or  waste. 

demands  of  artificial  appetite. 

Proper  Diet. 

Value  of  simple,  standard  foods. 
Objections  to  highly  seasoned  or  "  fancy  "  dishes. 
Importance  of  green  vegetables  for  mineral  salts. 
Concentrated  foods  not  good,  bulk  needed. 

Cooking. 

Functions,  makes  food  more  easily  digested. 

makes  food  more  appetizing. 

sterilizes  food. 

Faulty  cooking  may  make  food  less  digestible 
Boiling  vs.  pasteurizing  milk. 
Effect  of  cooking  on  teeth. 

No  Foods  for  Special  Organs. 
Lipoid. 
Vitamin  es. 
Dietary  Diseases. 


CHAPTER  XXXVIII 
NUTRITION 

Vocabulary 

Nutrition,  all  processes  concerned  with  building  up  tissue. 

Alimentary,  pertaining  to  food  or  nutrition. 

Fallacy,  a  mistaken  idea. 

Distended,  swelled  up  or  expanded. 

Lacteals,  lymph  capillaries  of  the  intestine  which  absorb  fat. 

Someone  has  said,  "  We  live,  not  on  what  we  eat,  but  on  what 
we  digest."  Food,  even  after  cooking,  is  not  usually  in  condition 
to  be  made  into  tissue  or  to  furnish  energy. 

Digestion  produces  two  important  changes  in  foods.  First,  it 
makes  them  soluble  to  allow  transfer  by  osmosis;  second,  it  changes 
them  chemically  to  permit  them  to  be  assimilated.  These  changes 
are  brought  about  in  two  ways,  first,  mechanically  by  the  teeth, 
the  motion  of  the  stomach,  and  intestinal  walls,  second,  chemically 
by  active  substances  in  the  digestive  fluids,  called  enzymes  or 
ferments.  The  latter  are  the  more  important  means  of  digestion; 
there  are  several  kinds,  each  acting  on  a  particular  foodstuff  and 
each  secreted  by  different  glands  in  various  parts  of  the  digestive 
tract.  They  will  be  referred  to  later  when  these  different  regions 
are  studied. 

Digestive  Organs.  The  digestive  tract  or  alimentary  canal  is 
practically  a  continuous  tube  with  many  glands  opening  into  it  to 
furnish  digestive  fluids,  also  with  a  rich  blood  supply  to  provide 
for  its  activities  and  to  remove  digested  foods.  This  food  tube 
consists  of  three  general  regions  whose  structure  and  functions  will 
be  studied  in  order, 

1.  The  mouth 

2.  The  gullet  and  stomach 

3.  The  intestines. 

363 


364 


BIOLOGY  FOR  BEGINNERS 


In  the  simpler  animals  the  digestive  canal  may  be  lacking 
(protozoa),  or  almost  straight  and  uniform  in  size  (worms),  but  in 


Salivary  &onef 


Vermiform  typemfa. 


FIG.  114.    Diagram  of  the  alimentary  canal.    Modified  from 
Landon's,  see  Kellogg. 

the  higher  animals  and  man  it  is  much  coiled  to  provide  greater 
surface  for  secretion  and  absorption,  and  also  varies  much  in 


NUTRITION  365 

diameter,  to  permit  the  carrying  out  of  special  functions  in  various 
parts. 

The  Mouth.  So  far  as  digestion  is  concerned,  the  mouth  per- 
forms two  functions:  in  it  the  food  is  crushed  or  cut  into  smaller 
portions  and  at  the  same  time  it  is  mixed  with  saliva,  one  of  the 
digestive  fluids,  whose  function  will  be  dealt  with  later.  The 
mouth  cavity  is  bounded  above  by  the  palate,  below  by  the  tongue, 
and  at  front  and  sides  by  the  teeth,  lips,  and  cheeks.  There  are 
six  openings  into  this  cavity,  from  within,  namely 

1.  Two  nasal  openings,  behind  the  palate  and  connecting  with 

the  nostrils,  above. 

2.  Two  eustachian  tubes,  also  far  back,  high  up  at  the  sides 

and  connecting  with  the  ears. 

3.  The  trachea  and  gullet  below,  the  former  in  front  and  con- 

necting with  the  lungs,  and  the  latter  behind  it  and  com- 
municating with  the  stomach. 

Other  organs  are  immediately  connected  with  the  mouth  cavity, 
most  of  which  can  be  seen  by  studying  your  own  mouth  with  a 
mirror  or  by  looking  into  a  friend's  mouth  with  a  small  electric 
light.  The  "  roof  of  the  mouth  "  or  hard  palate  can  be  easily 
recognized.  Back  of  it  is  a  downward  projecting  sheet  of  muscle, 
the  soft  palate;  at  either  side  rounded  projections  may  be  seen, 
which  are  tonsils. 

Behind  the  soft  palate  and  near  the  opening  into  the  nasal  cavity 
is  the  location  of  adenoid  growths  which  may  obstruct  the  breath- 
ing and  have  to  be  removed  if  they  reach  abnormal  size.  The 
tonsils  also  sometimes  become  enlarged  and  act  as  nests  for  bac- 
terial growth,  necessitating  their  removal.  Their  function  is  not 
thoroughly  understood,  and  when  diseased  their  removal  is  bene- 
ficial. 

The  openings  of  the  eustachian  tubes  are  protected  by  their 
high  location  and  by  folds  of  membrane  beside  them.  The  trachea 
is  protected  by  the  base  of  the  tongue  and  the  epiglottis,  which  is 
a  door-like  organ  that  covers  the  trachea  during  swallowing. 

The  Tongue.  The  tongue  is  easily  studied,  but  few  of  us  really 
know  its  shape,  size  or  structure.  The  best  way  to  find  out  is  to 


366 


BIOLOGY  FOR  BEGINNERS 


look  at  it.  It  is  a  large  muscular  organ,  nearly  filling  the  front 
part  of  the  mouth  cavity  when  the  jaws  are  closed.  It  has  great 
freedom  of  motion  and  performs  the  following  functions: 


FIG.  115.     Mouth  and  Throat. 

The  object  of  this  plate  is  to  show  the  relative  position  of  tue  organs  of  the 
nose  and  throat,  and  especially  to  indicate  the  course  taken  by  food  in  swal- 
lowing, and  air  in  breathing. 

Note  that  these  routes  cross  each  other,  making  necessary  the  adaptation 
mentioned  in  the  text,  to  prevent  food  from  entering  the  trachea  when  being 
swallowed. 

Attention  is  called  to  the  size  and  thickness  of  the  tongue,  which  we  usually 
think  of  as  long  and  thin.  Its  base  pushes  back  and  the  epiglottis  closes  down 
when  the  food  is  passing. 

Note  also  the  large  size  of  the  nasal  cavity  and  the  projecting  lobes  which 
help  warm  and  moisten  the  air,  catch  dust,  and  provide  surface  for  the  nerves 
of  smell. 

1.  It  is  the  organ  of  taste  —  a  sense  which  aids  in  selecting 
foods  and  in  promoting  their  digestion. 

2.  It  aids  in  chewing,  by  automatically  keeping  the  food  be- 
tween the  teeth. 

3.  It  is  concerned  in  the  process  of  swallowing,  since  it  rolls 


NUTRITION 


367 


.P.M 


the  food  into  proper  shape,  pushes  it  back  toward  the  gullet,  and 
partly  closes  the  trachea. 

4.  It  helps  to  keep  clean  the  inner  surface  of  the  teeth. 

5.  In  man  it  is  one  of  the  organs  concerned  in  speech. 
The  Teeth  Structure.    The  teeth 

are  even  more  familiar  and  im- 
portant organs.  Each  consists  of 
three  parts,  (1)  the  crown  or  ex- 
posed portion,  (2)  the  neck,  a  slight 
narrowing  at  the  edge  of  the  gum, 
and  (3)  the  root  or  roots  which  are 
attached  to  the  jaw, 

A  section  cut  lengthwise  through 
a  tooth  shows  that  the  crown  is 
covered  by  a  very  hard  substance 
called  enamel,  which  protects  the 
exposed  parts.  The  bulk  of  the 
tooth  consists  of  dentine,  a  softer 
and  more  porous  substance,  while 
the  center  is  occupied  by  the  pulp 
which  contains  the  nerves  and 
blood  vessels  of  the  tooth.  The 
root  is  covered  by  a  bone-like  coat- 
ing, the  cement,  and  through  the 
very  tip  is  'the  opening  by  which 
the  nerves  and  blood  vessels  find 
entrance. 

Number  and  Kinds  of  Teeth. 
It  is  easily  seen  that  there  are  four 
kinds  of  teeth  in  the  mouth  even 
though  the  full  number  may  not  be  there  till  the  20th  year. 

In  the  full  set  there  are  thirty-two,  sixteen  on  each  jaw,  arranged 
as  follows:  In  front  are  eight  incisors  with  sharp  edges,  whose 
function  is  to  cut  the  food,  next  on  each  side  is  one  canine,  or  four 
in  all,  which  are  pointed  and  which  the  lower  animals  use  for  tear- 
ing food.  In  man  they  assist  the  incisors.  Behind  these  on  each 


FIG.  116.  Vertical  section  of  a 
tooth  in  jaw.  E,  enamel ;  D,  dentine ; 
P  M ,  peridontal  membrane;  PC, 
pulp  cavity;  C,  cement;  B,  bone  of 
lower  jaw;  V,  vein;  A,  artery;  N, 
(After  Stirling.)  From 


368  BIOLOGY  FOR  BEGINNERS 

side  come  two  premolars  and  three  molars,  all  with  rough  flat 
crowns  and  used  to  crush  the  food.  The  first  or  "  milk  "  teeth 
lack  the  premolars  and  one  set  of  molars  hence  number  but  twenty 
in  all.  The  reason  for  having  two  sets  is  to  allow  for  the  growth 
of  the  jaw.  Hence,  if  the  first  teeth  are  allowed  to  decay  and  are 
pulled  too  soon,  the  jaw  never  gets  its  proper  shape  and  the  later 
teeth  are  crowded  and  irregular.  At  the  proper  times  the  roots  of 
the  first  teeth  are  absorbed  and  they  make  way  easily  for  the 
permanent  teeth  and  the  jaw  is  developed  into  proper  shape. 

The  numbers  of  teeth  are  often  expressed  in  fractional  form, 
and  are  easily  remembered  in  this  way.  Beginning  at  the  front  in 
the  middle  of  the  jaw  and  putting  the  upper  teeth  above  and  the 
lower  teeth  below,  we  have  the  "  dental  formula  "  for  the  adult 
and  first  sets  as  follows-: 

Incisors       Canines       Premolars      Molars 
First  set  (20)  '        f  }    '  jj  | 

2123 
Permanent  set  (32) 

L  \  L  o 

The  last  pair  of  molars  may  not  appear  till  about  the  20th  year 
and  are  therefore  called  the  wisdom  teeth,  as  one  is  supposed  to 
have  acquired  some  wisdom  by  that  time. 

Among  other  animals  the  teeth  vary  a  great  deal  in  size  and 
number,  but  there  is  none  that  has  a  greater  variety  of  kinds. 
Horses  and  cattle  have  molars  greatly  developed,  cats  and  dogs 
have  canines  long  and  sharp,  while  rats  and  squirrels  develop  the 
incisors  excessively  for  gnawing.  Vegetable  foods  require  broad 
grinding  teeth,  animal  food  needs  sharp  canines  and  shear-cutting 
premolars,  while  man,  being  adapted  for  a  mixed  diet,  has  all  forms 
moderately  developed.  Chewing  is  one  of  the  mechanical  processes 
which  prepares  the  food  for  chemical  action  by  the  digestive 
fluids. 

Glands.  Digestive  fluids  are  secreted  by  organs  called  glands. 
A  gland  consists  of  a  group  of  cells  adapted  for  producing  a  fluid 


NUTRITION 


369 


secretion.  These  cells  are  developed  on  the  inner  walls  of  a  cavity 
which  usually  opens  into  some  other  organ  by  way  of  a  tube  called 
a  duct. 

These  cavities  may  be  simple  and  very  small,  like  the  mucous 
glands  that  moisten  all  the  digestive  tract,  or  they  may  be  very 
large  and  complex  like  the  liver.  In  either  case  they  must  have  a 
rich  blood  supply  and  nerves  to  control  it  and  the  action  of  the 


TEMPORARY   SET.— > 
PERMANENT     SET 


CHART      S  H  O  W  INfr      ORDER 

SUCCESSION    AMD    Tine    OF   rut 

CE        OF      TEETH 


2>.\  IL^A       \pRE-\ 

Jfca 

nOLM 

-i  \ 

MOLAR 

MOLAR 

OF     THE 

H  E 

MOLAR 

FIG.  117. 

gland,  as  well.    A  gland,  then,  consists  of  the  secreting  cells,  the 
gland  cavity,  the  ducts,  the  blood  and  nerve  supply. 

Salivary  Glands.  The  principal  glands  of  the  mouth  are  the 
salivary  glands  of  which  there  are  three  pairs.  The  largest  pair  is 
located  beneath  the  ear  on  each  side  of  the  head  and  the  ducts  open 
opposite  the  second  upper  molar.  Inflammation  of  the  glands 
causes  the  mumps.  The  sub-maxillary  glands  lie  within  the  angles 
of  the  lower  jaw  and  the  sub-lingual  pair  are  below  the  tongue, 
beneath  the  floor  of  the  mouth;  ducts  from  both  pairs  open  under 
the  middle  of  the  tongue. 


370 


BIOLOGY  FOR  BEGINNERS 


•*  «S  TO  M  AC  H  *~ 


Saliva.  Saliva  is  a  thin,  alkaline  fluid  containing  the  enzyme 
ptyalin,  which  changes  starch  to  soluble  sugar,  but  this  action  is 
slight,  since  the  food  remains  so  short  a  time  in  the  mouth.  How- 
ever, the  other  functions  of  saliva  make  it  important  that  it  be 
thoroughly  mixed  with  the  food,  since  its  presence  in  the  stomach 
stimulates  the  gastric  glands.  It  also  permits  foods  to  be  tasted, 
since,  only  in  solution  will  the  food  affect  the  nerves  of  this  sense. 
Furthermore,  saliva  aids  in  chewing  and  is  indispensable  in  swal- 
lowing food,  so  that  its  digestive  function  is  only  one  of  several, 
and  the  quantity  secreted  is  much  greater  than  one  might  suppose, 
being  about  three  pints  per  day. 

The  steps  of  the  digestion  process  in  the  mouth,  then,  are 

1.  Food  mechanically  crushed. 

2.  Food  moistened  for  taste  and  swallowing. 

3.  Some  starch  changed  to  sugar*. 

4.  Very  slight  absorption  of  sugar,  water,  salts. 

The  Stomach.  Passing 
from  the  mouth,  the  food 
enters  the  gullet,  which  at 
a  distance  of  about  nine 
inches  enlarges  into  the 
stomach.  This  organ  is 
located  just  beneath  the 
diaphragm  with  the  inlet 
at  the  left  and  close  to  the 
heart.  Except  when  fully 
distended  it  is  not  the 
smooth,  pear-shaped  organ 
usually  pictured,  but  may  be  collapsed  and  empty,  or  almost  any 
irregular  shape,  depending  on  its  contents,  and  muscular  move- 
ments. 

Its  function  is  very  largely  to  store  and  finely  divide  the  food. 
We  usually  eat  at  one  time  enough  food  to  last  for  several  hours. 
This  food  must  be  stored  somewhere  and  the  stomach  provides 
the  place.  Also,  chewing  has  only  partly  divided  the  food,  so  a 
second  function  of  the  stomach  is  to  furnish  the  mechanical  separa- 


Courtesy  of  Ginn  and  Company. 
FIG.  118.     From  Hough  and  Sedgwick. 


NUTRITION 


371 


tion  of  the  food  particles  by  the  churning  motion  of  its  muscular 
walls.  The  walls  are  also  provided  with  millions  of  simple  glands 
which  secrete  the  gastric  fluid  at  the  rate  of  five  to  ten  quarts  per 
day. 

Gastric  Fluid.  This  gastric  fluid  contains  hydrochloric  acid  and 
two  ferments,  rennin  and  pepsin.  The  rennin  acts  on  the  casein 
(milk  proteid)  changing  it  to  curd, 
in  which  form  it  is  more  easily 
digested  by  other  ferments. 

(Note:  rennin  is  used  to  "  start  " 
cheese  and  in  "  junket  tablets,"  the 
latter  made  from  calves'  stomachs.) 

Pepsin,  acting  only  in  the  presence 
of  an  acid,  changes  some  proteids  to 
soluble  peptones  and  also  dissolves 
much  connective  tissue,  thus  ex- 
posing a  greatly  increased  food  sur- 
face for  digestion  in  the  intestine. 
Do  not  get  the  idea,  that  all  or  even 

a  great  deal  of  proteid  food  is  com-  glan?,s   ™      maHn  soi^ac;  a' 

mouth  of  gland  leading  into  a  long 

pletely  digested  in  the  stomach;  in  wide  duct,  ft,  into  which  open  the 
fact,  as  fast  as  they  are  finely  terminal  divisions;  c,  connective 
divided,  many  proteids  are  dis- 
charged into  the  intestine  where  the 
pancreatic  fluid  completes  the  major  part  of  proteid  digestion. 
The  stomach,  then,  performs  four  functions,  namely: 

1.  It  acts  as  a  storage  for  food. 

2.  It  mechanically  divides  and  separates  food  particles. 

3.  Rennin  curdles  casein. 

4.  Pepsin  acts  on  some  proteid  and  connective  tissue. 

Thus  it  is  apparent  that  "  stomach  trouble  "  and  digestive 
trouble  may  not  mean  the  same  thing,  and  despite  the  common 
idea,  the  bulk  of  digestive  processes  do  not  take  place  in  the 
stomach  but  in  the  small  intestine. 

The  food  as  it  is  discharged  into  the  intestine  is  called  chyme 
and  consists  of 


FIG.    119.     Section    of  pyloric 


After  Piersoe. 


tissue  of  mucosa. 
See  Kellogg. 


372 


BIOLOGY  FOR  BEGINNERS 


1.  The  fats  all  unchanged. 

2.  Most  of  the  carbohydrates. 

3.  A  large  portion  of  the  proteids. 

4.  Some  sugars,  peptones  and  water,  which  were  not  absorbed 
in  the  stomach. 

It  is  evident  that,  so  far,  the  food  has  been  mainly  prepared  for 
digestion  rather  than  digested,  a  process  that  is  chiefly  accom- 
plished in  the  small  intestine. 

The  Intestine.  The  stomach  connects  with  the  small  intestine 
by  way  of  a  muscular  valve  (the  pylorus)  which  prevents  the  food 

from  passing  before  it  is 
thoroughly  broken  up  in  the 
stomach. 

The  intestine  is  the  most  im- 
portant portion  of  the  digestive 
tract,  and  consists  of  a  coiled 
tube  about  twenty-five  feet  in 
length.  The  part  next  the 
stomach  is  about  twenty  feet 
long,  about  one  inch  in  diameter 
and  is  called  the  small  intestine, 
while  the  remaining  five  feet  are 
over  two  inches  in  diameter  and 
are  called  the  large  intestine. 


FIG.  120.  Mucous  membrane  of 
the  small  intestine  of  the  dog.  A, 
artery;  B,  vein;  C,  capillaries;  D, 
lacteals;  E,  glands  of  Lieberkiihn; 
Ep.,  epithelial  tissue.  After^Cadiat. 
See  Kellogg. 


The  small  intestine  joins  the 
large  at  the  lower,  right  side  of 
the  abdomen,  and  at  this  point 
is  the  location  of  the  appendix. 
Inflammation  of  this  organ  is  called  appendicitis. 

Adaptations  for  Increase  of  Surface.  In  order  that  both  secre- 
tion of  fluids  and  absorption  of  food  may  go  on,  much  surface  (for 
osmosis)  is  required. 

For  this  increase  of  surface,  the  intestine  is  adapted  in  three 
ways: 

1.  Its  great  length  and  coiled  position  in  the  body. 

2.  Its  inner  lining  projects  in  creases  and  folds. 


NUTRITION  373 

3.  The  lining  of  the  small  intestine  is  thickly  covered  with 
microscopic  projections  (villi). 

The  villi  are  so  fine  and  so  numerous,  that,  under  a  lens,  the 
intestinal  lining  looks  like  a  piece  of  velvet.  By  these  means  the 
absorbing  surface  is  increased  five  times,  so  that  the  total  area  of 
the  intestine  is  not  less  than  twenty-five  square  feet,  or  about  twice 
as  great  as  that  of  the  skin. 

Muscular  Action.  The  intestinal  walls  are  provided  with  layers 
of  involuntary  muscles  which  perform  two  functions  by  their  con- 
traction and  expansion. 

1.  They  mix  and  separate  the  food,  thus  constantly  exposing  it 
to  digestive  action. 

2.  They  keep  the  food  moving  slowly  through  the  digestive 
canal. 

The  efficiency  of  digestion  and  absorption  depends  as  much 
upon  these  muscular  movements  as  upon  the  chemical  action  of 
the  digestive  fluids,  themselves.  To  provide  the  fluids  for  intestinal 
digestion  there  are  three  kinds  of  glands,  (1)  the  intestinal  glands, 
(2)  the  liver,  (3)  the  pancreas. 

Intestinal  Glands.  The  intestinal  glands  are  small,  simple  and 
very  numerous,  being  located  in  the  lining  among  the  villi.  They 
secrete  a  strongly  alkaline  fluid  containing  sodium  carbonate  and 
also  enzymes  that  act  on  starches  and  sugars.  This  sodium  car- 
bonate (and  other  alkalis  from  the  pancreatic  fluid)  combine  with 
part  of  the  fats,  forming  soaps,  which  are  soluble  and  are  thus 
absorbed. 

The  Liver.  The  liver  is  the  largest  gland  in  the  body.  It  is 
located  between  the  diaphragm  and  stomach,  thus  being  the  upper- 
most of  the  abdominal  organs.  The  secretion  of  the  liver  is  called 
bile  and  is  a  thick  brown  liquid,  of  which  about  one  quart  is 
produced  daily.  Bile  has  several  important  functions,  as 
follows: 

1.  Bile  is,  itself,  a  waste  substance,  removed  from  the  blood. 

2.  It  aids  in  digestion  and  absorption  of  fats. 

3.  It  stimulates  the  action  of  the  intestine. 

4.  It  tends  to  prevent  decay  of  intestinal  contents. 


374 


BIOLOGY  FOR  BEGINNERS 


ABSORPTION 


The  chief  digestive  action  of  the  bile  is  on  the  fats  which  it  makes 
into  a  milk-like  emulsion  to  be  absorbed  by  the  lacteals.  If  it  is 
prevented  from  entering  the  intestine,  over  half  of  the  fats  eaten 
are  not  absorbed. 

Another  important  function  of  the  liver  is  the  storage  of  excess 
carbohydrate  food,  in  the  form  of  glycogen  or  liver  starch  which 
the  body  may  draw  upon  as  a  source  of  energy  in  emergencies.  The 
liver,  then,  excretes  waste,  secretes  a  digestive  fluid,  and  stores  food. 
Pancreas.  Lying  between  the  lower  side  of  the  stomach  and 
the  first  fold  of  the  intestine  is  the  pancreas,  whose  secretion  is  by 

far  the  most  important  in  pro- 
ducing the  chemical  changes 
of  digestion.  The  pancreatic 
fluid  is  strongly  alkaline,  and 
contains  three  enzymes: 
trypsin,  amylopsin,  and  steap- 
sin. 

The  trypsin  resembles  pep- 
sin and  completes  the  digestion 
of  the  proteids,  changing  them 
into  soluble  peptones.  The 
amylopsin  (like  the  ptyalin  of 
saliva)  changes  starch  to  sugar, 
while  the  steapsin  changes  fats 
to  fatty  acids,  soluble  soaps, 
and  glycerin,  all  of  which  are 
easily  absorbed. 

FIG.  121.    Chart  showing  process  The    pancreatic   fluid    thus 

of  absorption.  completes  the  digestion  of  food 

after  it  has  undergone  the  pre- 
paratory steps  of  (1)  cooking,  (2)  chewing,  (3)  salivary  digestion, 
(4)  gastric  separation,  (5)  gastric  digestion. 

Absorption  and  Assimilation.    The  general  purpose  of  digestion 
is  to  put  the  foods  in  a  soluble  form  so  that  they  may  pass  through 
the  body's  membranes  by  osmosis. 
Absorption  is  the  name  given  to  the  passage  of  digested  food 


NUTRITION  375 

materials  from  the  digestive  tract  to  the  blood.  However,  absorp- 
tion in  a  living  animal  is  not  merely  a  mechanical  "  soaking  up  " 
of  prepared  foods,  but  other  changes  take  place,  as  the  products  of 
digestion  enter  the  circulation. 

Absorption  may  take  place  (1)  directly  into  the  blood  capillaries 
which  richly  supply  the  walls  of  the  stomach  and  intestine  or 
(2)  indirectly,  by  way  of  the  lymph  capillaries  of  the  villi  (lacteals) 
which  eventually  empty  into  the  blood  circulation  also. 

The  capillaries  of  the  gastric  vein  in  the  stomach  walls  absorb 
some  water,  a  little  digested  proteid,  and  still  less  sugar,  but  the 
principal  region  of  absorption  is  in  the  villi  of  the  small  intestine. 
Here  the  thin  walls  and  enormous  surface  bring  the  digested  foods 
close  to  the  blood  and  lymph  capillaries.  Peptones,  sugars  and 
fatty  acids,  salts  and  water  are  passed  into  the  blood  stream,  while 
the  fats  that  have  been  emulsified  are  taken  up  by  the  lymph  capil- 
laries (lacteals)  and  carried  by  the  lymphatic  circulation  to  the 
thoracic  duct  and  finally  emptied  into  the  general  circulation, 
near  the  left  jugular  vein. 

Assimilation.  All  the  steps  of  digestion  and  absorption  lead  to 
the  final  process  of  assimilation,  which  either  builds  up  the  cells 
or  supplies  them  with  energy.  For  this  purpose  the  blood  carries 
the  absorbed  foods  to  the  tissues.  These  foods  pass  as  lymph 
(by  osmosis)  from  the  capillaries  to  the  lymph  spaces  which  sur- 
round every  living  cell,  and  there  the  assimilation  occurs.  Every 
cell  of  the  body  is  practically  an  island,  bathed  on  every  side  by 
lymph,  which  brings  from  the  blood  the  digested  food  stuffs  (and 
oxygen  as  well)  and  removes  to  the  blood  stream  the  waste  matters 
produced  by  the  cells'  activities. 

Nutrition.  All  these  processes  by  which  food  is  obtained,  pre- 
pared, and  built  into  tissues,  are  grouped  together  as  nutrition 
and  include: 

1.  Food-getting,  selection,  and  preparation. 

2.  Digestion  .which  mainly  goes  on  in  mouth,  stomach,  and 
intestines. 

3.  Absorption  which  occurs  principally  in  the  small  intestine 
and  stomach,  by  means  of  the  blood  capillaries  and  lacteals. 


376 


BIOLOGY  FOR  BEGINNERS 


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NUTRITION  377 

4.  Assimilation  which  takes  place  wherever  there  is  a  living 
cell  to  be  nourished. 

Attention  should  be  called  to  the  important  part  played  by 
osmosis  in  all  these  processes.  It  is  concerned  in  the  secretion  of 
all  digestive  fluids;  in  the  absorption  of  digested  foods  through 
the  walls  of  the  capillaries  and  lacteals,  and  in  the  passage  of  these 
same  foods  outward  from  the  capillaries,  as  lymph,  in  assimilation. 

COLLATERAL   READING 

The  Body  at  Work,  Gulick,  pp.  149-172;  Civic  Biology  Hunter,  pp. 
296-312;  Human  Mechanism,  Hough  and  Sedgwick,  pp.  89-131;  Studies 
in  Physiology,  Peabody,  pp.  75-166;  Elementary  Physiology,  Huxley, 
pp.  249-303;  Applied  Physiology,  Overton,  pp.  51-73;  Physiology  for  Be- 
ginners, Foster  and  Shore,  pp.  128-156;  The  Human  Body,  Martin,  pp. 
106-146;  General  Physiology,  Eddy,  pp.  90-158;  Physiology  Textbook, 
Colton,  pp.  194-231;  Human  Body  and  Health,  Davidson,  pp,  76-105; 
High  School  Physiology,  Hughes,  pp.  87-142. 


SUMMARY 
Digestive  Changes. 

1.  Making  food  soluble  (for  osmosis). 

2.  Changing  food  chemically  (for  assimilation). 

3.  Changes  caused  by 

(a)  Mechanical  action  of  teeth  and  stomach. 

(b)  Chemical  action  of  fluids,  enzymes,  ferments. 

Digestive  organs  (cf.  with  other  animals). 

1.  Mouth 

2.  Gullet  and  stomach. 

3.  Intestine. 

Mouth. 

Functions  in  digestion. 

1.  Mechanical  (chewing). 

2.  Chemical  (saliva). 
Openings  and  organs. 

1.  Nasal  openings  (2),  where,  how  protected,  into  what. 

2.  Eustachian  tubes  (2),  where,  how  protected,  into  what. 

3.  Trachea  (relation  of  epiglottis  and  tongue). 

4.  Gullet. 

5.  Hard  and  soft  palate. 

6.  Tonsils,  adenoids. 


378 


BIOLOGY  FOR  BEGINNERS 


Tongue. 

Structure,  size,  position  in  mouth. 
Functions. 

1.  Taste  (what  use  for  taste,  where  located). 

2.  Aid  in  chewing.     Aid  in  swallowing. 

3.  Cleaning  teeth. 

4.  Speech. 
Teeth. 

;  Parts.    Crown,  neck,  root  (make  diagram). 
Structure. 

1.  Enamel  (structure  and  function). 

2.  Dentine  (structure  and  function). 

3.  Pulp  region,  nerves,  and  blood  supply  (why  each). 
Kinds: 


Number 

Name 

Structure 

Function 

1st 

2nd 

Incisors 

8 

8 

Canines 

4 

4 

Premolars 

0 

8 

Molars 

8 

12 

Why  two  sets  of  teeth? 

How  does  the  change  take  place? 

Special  tooth  adaptations  in  other  animals, 
Glands  in  general. 

Definition. 

Parts,  secreting  cells  and  ducts,  blood  and  nerve  supply. 

Various  degrees  of  complexity. 
Salivary  glands. 

1.  Parotid  (where  located,  duct  opening),  mumps. 

2.  Sub-maxillary. 

3.  Sub-lingual. 
Saliva. 

Composition,  alkaline,  watery,  three  pints  daily,  ptyalin. 
Functions. 

1.  Aids  in  tasting  food  (solution). 

2.  Aids  in  swallowing. 

3.  Stimulates  gastric  glands  (alkali  vs.  acid). 

4.  Ptyalin  acts  on  starches  slightly. 
Digestive  changes  in  the  mouth. 

1.  Food  mechanically  crushed. 

2.  Moistened  for  taste  and  swallowing. 


3.  Some  starch  changed  to  sugar. 

4.  Slight  absorption  of  water,  sugar 


NUTRITION  379 

etc. 


Stomach. 

Location. 
Shape  and  size. 
Functions. 

1.  Storage  (why,  what  homologous  organs). 

2.  Further  separation  of  food  particles. 

3.  Digestion  of  proteids  by  means  of  pepsin. 

4.  Coagulation  of  milk  casein. 
Gastric  fluid. 

1.  From  gastric  (simple)  glands,  acid  glands. 

2.  Amount,  secretion  aided  by  saliva  if  well  mixed. 

3.  Composition '  Function 

Hydrochloric  acid  Neutralize  saliva,  aid  pepsin. 

Pepsin  Proteid  to  peptone. 

Dissolves  connective  tissue. 

Exposes  more  surface  for  digestion. 

Rennin  Coagulates  milk  proteid  (casein). 

Composition  of  chyme. 

1.  All  fats  unchanged. 

2.  Most  carbohydrates  (what  exception?). 

3.  Much  unchanged  proteid. 

4.  Un-absorbed  peptones,  sugars,  water,  etc. 

Intestine. 

Pylorus,  location  and  function. 

Parts,  small,  large,  colon,  rectum,  etc.  (need  not  learn). 

Appendix  (lower  right  side). 

Adaptations  for  increase  of  surface' (for  osmosis  for  absorption). 
Length,  25  ft.,  much  coiled. 
Walls  in-folded. 

Villi  (each  with  blood  vessels  and  lacteals). 
Surface  increased  five  times,  twice  area  of  skin. 
Muscular  intestinal  walls. 
Muscles  involuntary. 
Keep  food  moving  along. 
Mix  food  with  fluids  and  crush  it. 
Very  important  in  digestion. 
Glands. 
Intestinal. 

Small,  simple,  numerous,  in  the  intestine  wall  lining. 
Secretion,  alkaline;  soda  carbonate;  sugar  ferment. 
Function,  saponify  fats,  act  on  sugar  somewhat. 
Liver. 

Largest  gland,  uppermost  in  viscera,  over  stomach. 
Bile,  thick,  brown,  one  quart  daily. 


380 


BIOLOGY  FOR  BEGINNERS 


Functions,  waste. 

Aids  digestion  and  absorption  of  fats. 

Stimulates  intestinal  action. 

Antiseptic  action. 
General  functions. 
Excretion  of  waste. 
Secretion  of  a  digestive  fluid. 
Storage  of  sugar  excess  as  glycogen  (why?). 
Pancreas,  location. 

Fluid,  abundant,  alkaline. 
Composition. 

Ferment  changes         [to] 

Amylopsin  starch 

Trypsin  proteid 

Steapsin  fats 


soluble 
sugar 
peptone. 

fat  acids,  soaps,  glyc- 
erin. 


Preparatory  steps  in  nutrition. 

Food-getting,  cooking,  chewing. 

Salivary  digestion,  gastric  digestion  (further  breaking  up). 
Intestinal  digestion  (most  important). 
What  processes  are  these  steps  a  preparation  for? 
Absorption. 

What  is  the  general  purpose  of  digestion? 

What  is  the  process  on  which  absorption  is  based? 

Absorption  is  the  passage  of  food  from  digestive  tract  to  blood. 

May  take  place, 

1.  Directly  into  capillaries  in  stomach  and  intestine  walls. 

2.  Via  lymph  capillaries  (lacteals)  in  villi. 


Absorbing  organs 

Where 

What  absorbed 

Where  emptied 

Gastric  capillaries 

In  stomach  walls 

Water 
Peptones 
Sugar 

General  circulation 
via  gastric  vein 

Intestinal  capillaries 

In  villi 

Peptones 

Sugars 
Fatty  acids 
Water,  salts 

General  circulation 
via  mesenteric 
vein 

Lacteals   or   lymph 
capillaries 

In  villi 

Emulsified  fats 

Thoracic  duct  to 
left  jugular  vein 

Assimilation. 

Meaning  of  word. 
Definition. 


NUTRITION  381 

Course  of  digested  food. 

Digestive  organs  to 

Blood  stream  (osmosis). 

Through  capillary  walls. 

Into  lymph  spaces  (osmosis). 

Built  into  cell  substance. 

Blood  transports  food,  etc.,  to  tissues  via  capillaries. 
Lymph  transports  foods,  etc.,  to  cells  after  leaving  the  capillaries. 
Nutritive  processes  Where  performed. 

1.  Food-getting,  preparation 

2.  Digestion.  Mouth,  stomach,  intestine. 

3.  Absorption.  Stomach,  small  intestine  by  capil- 

laries and  lacteals. 

4.  Assimilation.  In  all  living  cells. 


CHAPTER  XXXIX 

RESPIRATION 

Vocabulary 

Lymph,  the  liquid  part  of  the  blood,  in  contact  with  cells. 

Pleural  membranes,  a  double  membrane  covering  lungs. 

Intermittent,  not  continuous. 

Depression,  lowering. 

Haemoglobin,  the  red,  oxygen-carrying  part  of  the  blood. 

Respiration  is  the  process  by  which  each  cell  of  the  body  takes 
in  oxygen  and  gives  off  carbon  dioxide  and  water.  It  is  tissue  oxi- 
dation. The  breathing  movements,  which  renew  the  air  in  the  lungs, 
and  the  circulation  of  blood,  which  is  the  means  of  transportation 
between  lungs  and  tissues,  are  merely  helps  in  the  real  process  of 
respiration  which  goes  on  in  every  cell  of  the  body. 

Need  of  Circulation.  These  breathing  and  circulatory  processes 
are  required  because  of  the  distance  of  the  living  cells  from  the 
outer  air  and  merely  serve  to  keep  the  lymph  supplied  with  oxygen 
and  freed  from  waste.  It  is  between  the  lymph  and  each  living  cell, 
that  respiration  actually  goes  on. 

The  organs  generally  associated  with  respiration,  such  as  the 
lungs,  trachea,  etc.,  are  really  concerned  with  supplying  oxygen  to 
the  blood  and  removing  wastes.  No  more  actual  respiration  (cell 
oxidation)  goes  on  in  the  lungs,  than  in  any  other  active  tissue, 
but  it  is  in  the  lungs  that  the  haemoglobin  of  the  blood  receives  its 
load  of  oxygen  and  unloads  its  carbon  dioxide  and  water. 

Development  of  Respiration.  Respiration  in  the  protozoa  took 
place  by  direct  contact  of  each  cell  with  the  air  dissolved  in  the 
water.  In  the  worms  the  blood  circulated  in  the  skin  and  obtained 
its  oxygen  direct  from  the  air.  In  still  higher  forms,  like  crayfish 
or  fish,  gills  were  developed  with  great  extent  of  surface  to  absorb 

382 


RESPIRATION 


383 


the  dissolved  oxygen  in  the  water.  Insects  took  their  air  directly 
into  the  tissues  and  blood  by  way  of  their  numerous  complicated 
air  tubes  and  so  got  along  with  a  simple  circulation.  In  the  birds 
and  mammals  this  is  reversed  and  the  air  comes  to  one  place  only 


FIG.  122.  Bronchi  and  lungs,  posterior  view,  showing  position  of  heart. 
1,  1,  summit  of  lungs;  2,  2,  base  of  lungs;  3,  trachea;  4,  right  bronchus;  5, 
branch  to  upper  lobe  of  lung;  6,  branch  to  lower  lobe;  7,  left  bronchus;  8, 
branch  to  upper  lobe;  9,  branch  to  lower  lobe;  10,  left  branch  of  pulmonary 
artery;  11,  right  branch;  12,  left  auricle  of  heart;  13,  left  superior  pulmonary 
vein;  14,  left  inferior  pulmonary  vein;  15,  right  superior  pulmonary  vein; 
16,  right  inferior  pulmonary  vein;  17,  inferior  vena  cava;  18,  left  auricle  of 
heart;  19,  right  ventricle.  (After  Sappey.)  From  Kellogg. 

(the  lungs),  while  a  complex  circulation  carries  the  oxygen  to  all 
parts  of  the  body. 

Organs  of  Breathing.  The  organs  concerned  with  breathing 
motions  can  be  placed  in  two  groups,  (1)  those  concerned  with 
holding  and  carrying  the  air,  and  (2)  those  which  change  the  size 
of  the  chest  cavity,  causing  the  air  to  circulate. 


384  BIOLOGY   FOR  BEGINNERS 

Nose.  The  air  system  begins  with  the  nose,  which  is  adapted  as 
an  entrance  for  air, 

(1)  By  the  hairs  and  moist  mucus  to  catch  dust. 

(2)  By  the  sense  of  smell  to  guard  against  bad  air. 

(3)  By  its  long  moist  passages  which  warm  and  moisten  the  air. 
The  mouth  was  not  intended  as  a  breathing  organ  except  in 

emergencies,  and  habitual  mouth  breathers  lose  all  the  advantages 
mentioned  above. 

Trachea.  Passing  from  the  nasal  cavity  to  the  back  of  the  mouth, 
the  air  enters  the  trachea.  This  is  a  large  tube  which  opens  into 
the  mouth  at  the  back  of  the  tongue,  so  that  the  food  passes  over 
it  when  we  swallow.  Its  upper  end  is  therefore  protected  by  the" 
base  of  the  tongue  and  by  a  sort  of  self-acting  lid  (epiglottis) 
which  closes  when  food  is  passing  on  its  way  to  the  gullet,  which  is 
further  back  in  the  mouth  cavity.  The  enlarged  upper  end  of  the 
trachea  is  the  larynx  in  which  are  situated  the  vocal  (speech)  or- 
gans, and  which  may  be  seen  externally  as  the  "  Adam's  apple." 
The  walls  of  the  trachea  are  supported  by  rings  of  cartilage,  which 
hold  it  open  for  free  passage  of  air. 

With  the  hand  on  the  larynx,  swallow  a  mouthful  of  food  and 
notice  two  things,  (1)  how  it  rises  and  contracts  inward  to  meet 
the  epiglottis,  (2)  how  the  very  base  of  the  tongue  moves  back  and 
down  over  the  opening.  Both  these  movements  are  to  allow  the 
food  to  pass  over  the  top  of  the  trachea  and  into  the  gullet. 

Bronchi  and  Air  Cells.  At  its  lower  end  the  trachea  divides  into 
two  branches  (bronchi)  extending  to  each  lung,  where  they  sub- 
divide into  countless  minute  bronchial  tubes  which  finally  terminate 
in  very  thin-walled,  elastic  air  cells  of  which  the  lung  tissue  is 
largely  made.  Thus  there  is  provided  in  one  organ  (the  lungs) 
enough  surface  for  air  osmosis  to  supply  (via  blood)  the  needs  of 
the  millions  of  body  cells  that  have  no  direct  access  to  air. 

The  Lungs.  The  lungs  fill  all  the  body  cavity  from  the  shoulders 
to  the  diaphragm  except  the  space  occupied  by  the  heart  and  blood 
vessels.  They  are  very  spongy,  consisting  mainly  of  the  air  tubes 
and  cells  and  a  very  extensive  network  of  blood  vessels  and  capil- 
laries, all  held  together  by  connective  tissue  and  covered  on  the 


RESPIRATION 


385 


outside  by  a  double  (pleura!)  membrane.  Their  shape  is  the  same 
as  the  chest  cavity,  the  upper  part  of  which  they  completely  fill. 
Between  them  is  the  heart  and  below  is  the  diaphragm  which 
is  a  muscular  partition  curving  upward  so  that  the  lower  lung 
surface  is  sharply  concave.  The  pleura]  membrane  that  covers 
the  lungs  and  lines  the  chest  cavity  is  constantly  moist  and  per- 
mits free  motion  of  the  lungs,  within  the  chest,  for  breathing. 


?ui.noMATiy  A  fir. 


TUBE 

T~o  PULMOMAHY  Vei 


-BLOOD 


Fid.  123.     Exchanges  between  blood  and  air  in  lungs.     After  Colton. 


Pleurisy  is  an  inflamed  condition  of  these  membranes  which  makes 
breathing  very  painful  and  difficult. 

Blood  Supply.  The  pulmonary  artery  brings  the  dark  (de-oxy- 
genated) blood  to  the  lungs,  where  it  divides  into  an  extensive 
network  of  capillaries,  completely  surrounding  each  air  cell.  The 
thin  walls  of  both  cell  and  capillary  make  easy  the  osmotic  ex- 
change of  oxygen  from  air  to  blood,  and  of  carbon  dioxide  and 
water  from  blood  to  air,  so  that  the  pulmonary  vein  returns  its 
blood  to  the  heart,  purified  and  laden  with  oxygen  for  the  tissues. 


386 


BIOLOGY  FOR  BEGINNERS 


Air  Capacity.  The  total  capacity  of  the  lungs  is  about  350  cubic 
inches  of  which  our  ordinary  breathing  utilizes  but  about  30.  By 
extra  effort  we  can  take  in  and  force  out  an  extra  hundred  or  more, 
while  there  is  about  another  hundred  cubic  inches  which  we  can- 
not get  out  at  any  one  breath.  When  we  realize  the  great  import- 
ance of  oxygen  to  the  tissues  these  facts  ought  to  be  an  argument 
for  fresh  air,  deep  breathing,  and  loose  clothing.  We  use  little 
RESP.RAT.OH  CHART.  enough  of  our  lungs,  at 

best,  so  every  effort  ought 

, „         to   be   made    to    increase 

their  activity.  The  one- 
third  of  the  air  which  can- 
not be  forced  out  of  the 
lungs  provides  for  continu- 
ous osmosis.  Breathing  is 
an  intermittent  process  but 
the  blood's  supply  of  air 
has  to  be  continuous, 
hence  the  need  for  some 
air  always  in  the  lungs. 
A  reason  for  deep  breath- 


(30 


FIG.  124.  Compare  capacity  utilized  by 
ordinary  breathing  with  that  of  deep 
breathing. 


ing  is  to  mix  as  much 
fresh  air  with  this  "  resi- 
dual air  "  as  is  possible 
at  each  breath. 

Breathing  Movements;  The  process  of  getting  air  into  and 
out  from  the  lungs  is  rather  complicated  and  consists  of  two  sets 
of  operations,  inspiration  (breathing  in)  and  expiration  (breath- 
ing out)  which  we  somewhat  wrongly  call  the  acts  of  respira- 
tion. 

Inspiration:  The  Diaphragm.  The  chief  breathing  organ  is  the 
diaphragm,  a  muscle  (not  a  mere  partition)  which  extends  across 
the  body,  curving  upward,  as  a  floor  to  the  lung  cavity.  When 
its  muscles  contract  it  tends  to  pull  down  straighter  across  the  body, 
thus  giving  the  lungs  more  room,  but  compressing  the  abdominal 
organs  beneath  it  at  the  same  time. 


RESPIRATION 


387 


Rib  Muscles.  Second  in  importance  are  muscles  between  the 
ribs  which  lift  them  up  and  outward,  thus  enlarging  the  lung  cavity, 
but,  which  is  more  important,  bending  the  elastic  rib  cartilages, 
which  tend  to  spring  the  ribs  back  in  place. 

Air  Pressure.  The  third  important  factor  in  inspiration  is  the 
pressure  of  the  outside  air 
which  rushes  in  to  occupy 
the  extra  space  thus  pro- 
vided and  by  so  doing, 
expands  the  elastic  tissue 
of  the  lungs.  Inspiration, 
then,  consists  of  (1)  de- 
pression of  diaphragm  and 
compression  of  abdominal 
organs,  (2)  raising  the 
ribs  and  bending  the  rib 
cartilages,  (3)  air  pressure, 
expanding  the  lung  tissue. 

Expiration.  Expiration 
is  merely  the  springing 
back  of  the  organs  that 
have  been  compressed  by 
the  movements  of  inspira- 
tion. It  consists  of  the 
following  steps:  (1)  the 
elastic  reaction  of  the  com- 
pressed abdominal  organs, 
(2)  the  springing  back  of 
the  rib  cartilages,  (3)  the 


I 


FIG.  125.  Lower  half  of  thorax  with 
dorsal  and  lumbar  vertebrae.  A,  sixth 
dorsal  vertebra;  Ao,  aorta;  D,  (lower) 
diaphragm;  D,  (upper)  aorta  passing 
through  diaphragm;  /,  intercostal  muscles; 
O,  cesophagus;  IV,  opening  in  diaphragm 
for  vena  cava  ascending;  T  T,  tendons  of 
right  and  left  crura  attaching  diaphragm 
to  3rd  and  4th  lumbar  vertebrae.  (After 
Allen  Thomson.)  From  Kellogg. 


contraction  of  the  elastic 
lung  tissue. 

All  of  these  tend  to  make  the  lung  capacity  less  and  force  out 
the  air,  against  its  own  pressure.  The  change  of  position  of  the  ribs, 
diaphragm  and  abdominal  organs  can  be  felt  in  our  own  bodies. 

Rate  of  Breathing.  This  double  process  takes  place  from  16  to 
24  times  per  minute,  depending  upon  activity,  position,  and  age. 


388 


BIOLOGY  FOR  BEGINNERS 


The  more  oxygen  the  tissues  need,  the  more  rapidly  the  lungs  have 
to  operate  to  supply  the  blood  with  it,  to  be  carried  to  the  tissues. 
Air  Changes  in  Breathing.  Air  contains  only  about  20  per  cent 
of  oxygen.  Of  this,  only  about  a  quarter  is  absorbed  in  the  lungs 
by  the  haemoglobin  of  the  blood.  In  the  circulation,  the  haemo- 
globin can  give  out  only  about  one-half  the  oxygen  it  contains,  so, 


FIG.  126.  Diagram  to  show  the  changes  in  the  sternum,  diaphragm,  and 
abdominal  wall  in  respiration.  A,  inspiration;  B,  expiration;  Tr,  trachea; 
St,  sternum;  D,  diaphragm;  Ab,  abdominal  wall.  The  shaded  part  is  to  indi- 
cate the  stationary  air.  From  Martin- Fitz. 


unless  we  breath  deeply  and  keep  our  breathing  apparatus  in 
healthy  working  order,  the  tissues  may  receive  too  little  oxygen. 
Since  oxidation  (union  of  oxygen  with  tissue)  is  the  only  source 
of  life  energy,  this  matter  is  of  very  great  importance. 

Expired  air  loses  about  one-fourth  of  its  oxygen,  but  receives 
100  times  as  much  carbon  dioxide  as  it  had  when  taken  in,  also  a 


RESPIRATION  389 

large  amount  of  water  vapor  and  heat,  together  with  a  very  little 
organic  waste  matter. 

Ventilation.  The  fact  that  air  in  a  "  close  "  room  becomes  un- 
fit to  breathe,  is  due  mainly  to  the  excess  moisture  and  heat,  and 
not  to  the  carbon  dioxide,  or  lack  of  oxygen,  as  was  formerly  sup- 
posed. 

The  carbon  dioxide  in  the  expired  air  is  produced  by  the  oxygen 
from  the  lymph  uniting  with  the  carbon  of  the  tissues.  The  water 
is  produced  by  oxidation  of  their  hydrogen,  and  the  heat  is  the 
result  of  both  oxidation  processes.  We  use  annually  about  10,000 
pounds  of  air  (28.7  pounds  per  day)  from  which  we  take  about 
650  pounds  of  oxygen  and  give  off  about  730  pounds  of  carbon 
dioxide.  We  breathe  out  about  9  ounces  of  water  every  day,  which 
would  make  half  a  pint  in  liquid  form.  These  figures,  while  not 
worth  remembering,  will  give  some  idea  of  the  amount  of  work 
done  by  the  respiratory  organs  and  their  importance  to  our  life. 

Proper  ventilation  is  concerned,  not  only  with  supplying  "  fresh  " 
air,  but  with  the  removal  of  water  vapor,  heat,  and  least  of  all, 
carbon  dioxide.  Here  circulation  of  air  in  a  room  will  often  relieve 
breathing  conditions,  by  lowering  the  body  temperature  and  re- 
moving excess  water  vapor  from  the  vicinity  of  the  body.  We 
usually  have  oxygen  enough  in  any  ordinary  air  supply,  and  seldom 
does  the  carbon  dioxide  cause  trouble,  but  very  often  the  tem- 
perature and  amount  of  water  vapor  produce  unpleasant  and  even 
dangerous  results. 

COLLATERAL  READING 

Physiology  Textbook,  Colton,  pp.  105-137;  General  Physiology,  Eddy, 
pp.  312-339;  Applied  Physiology,  Overton,  pp.  206-219;  Human  Mecha- 
nism, Hough  and  Sedgwick,  pp.  162-176;  Human  Body  and  Health,  Davison, 
pp.  132-162;  Studies  in  Physiology,  Peabody,  pp.  209-231;  Human  Body, 
Martin,  pp.  193-214;  Elementary  Physiology,  Huxley,  pp.  148-191;  High 
School  Physiology,  Hughes,  pp.  179-196; 


390  BIOLOGY  FOR  BEGINNERS 

SUMMARY 

Definition,  Respiration  is  oxidation  in  the  tissues. 

Aided  by  "  breathing  movements  "  (oxygen  from  air  to  blood). 
Circulation  (oxygen  from  blood,  to  lymph,  to  tissues). 
Lungs  supply  osmotic  surface  for  all  cells  in  one  place. 
Circulation  transports  oxygen  to  interior  tissues. 

Development  in  lower  animals. 

Protozoa,  each  cell  in  contact  with  dissolved  oxygen. 
Worms,-  blood  in  contact  with  air  in  skin. 
Crayfish,  blood  in  contact  with  dissolved  air  (gills). 
Insect,  air  brought  to  blood  and  tissues  in  tubes  (tracheae). 
Fish,  blood  in  contact  with  dissolved  air  (gills). 
Other  vertebrates,  blood  aerated  in  lungs. 

Organs  of  breathing. 

1.  Nose,  adaptations,  hairs  to  collect  dust. 

Smell,  to  detect  bad  air. 
Moistening  mucous  membranes. 

2.  Trachea. 

Connects  mouth  and  lungs. 
Opens  back  of  tongue. 

Stiffened  by  cartilage,  larynx  with  vocal  organs. 
Protected  by 
Epiglottis. 

Movements  of  tongue  in  swallowing. 
Movements  of  larynx  in  swallowing. 
Mucous  glands  and  cilia. 

3.  Bronchi. 

Two  branches  of  trachea  to  lungs. 

Each  with  many  small  branches. 

Air  cells  at  end  of  branches,  vastly  numerous. 

4.  Lungs. 

Location,     shape,  boundaries. 
Structure. 

Air  tubes  and  cells  .  .  .  surface  for  osmosis. 

Capillaries  .  .  .  blood  for  transfer 

Pleural  membranes  .  .  .  moist  for  easy  motion. 
Blood  supply. 

Pulmonary  arteries  .  .  .  dark,  deoxygenated  blood. 

Pulmonary  veins  . .  .  lighter,  oxygenated  blood. 
Capacity. 

350  cu.  in.  total. 

250  cu.  in.  possibly  used. 

30  cu.  in.  usually  used  in  ordinary  breath. 

100  cu.  in.  residual  air.     Reason  for  "residual  air." 


RESPIRATION  391 

Breathing  movements 

Inspiration  (increases  chest  cavity). 

(1)  Diaphragm  contracts  and  lowers  (vs.  abdominal  organs). 

(2)  Rib  muscles  raise  ribs  (vs.  elastic  cartilage). 

(3)  Air  pressure  expands  cells  (vs.  elastic  walls). 
Expiration  (decreases  chest  cavity). 

(1)  Abdominal  organs  push  diaphragm  upward. 

(2)  Rib  cartilages  spring  back. 

(3)  Lung  cells  contract. 

Rate,  16-24  per  minute,  depends  on  age,  activity,  etc. 
Air  changes  in  breathing. 

Air  contains 

Before  inspiration  After  inspiration 

79  %  Nitrogen  79  % 

20.96%  Oxygen  16.02% 

.04  %  Carbon  dioxide  4.38  % 

traces  Water  vapor  .60  % 

little  Heat  much  more, 

none  Organic  impurities    considerable. 

Blood  changes  in  lungs. 

Just  the  reverse  of  the  above. 

Blood  gains  4  to  5  %  oxygen. 
Blood  loses  about  same  amount  carbon  dioxide. 

Blood  loses  water  vapor,  heat,  organic  waste. 
Ventilation. 

Large  amount  of  air  used. 

Importance  of  oxidation. 

Need  for  ventilation  to  supply  oxygen. 

to  remove  heat,  water  vapor,  carbon  dioxide. 


CHAPTER  XL 
CIRCULATION 

Vocabulary 

Transportation,  carrying  from  place  to  place. 
Plasma,  liquid  portion  of  blood  tissue. 
Auricles,  upper,  receiving  chambers  of  the  heart. 
Ventricles,  lower,  sending  chambers  of  the  heart. 

The  function  of  any  circulatory  system  is  transportation;  the 
blood  is  the  carrier,  the  blood  vessels  are  the  roads,  and  the  heart 
is  the  motive  power.  Digested  food  is  carried  from  the  digestive 
organs  to  the  tissues,  oxygen  from  the  lungs  to  the  tissues,  waste 
matters  from  the  tissues  to  the  lungs,  skin,  and  kidneys,  and  in- 
ternal secretions  from  their  glands  to  places  where  they  are  used. 

Development  of  Circulation.  A  circulatory  system  is  not  found 
in  very  simple  animals  like  protozoa,  sponges,  and  hydra,  because 
they  have  so  few  cells  that  each  can  obtain  its  own  food  and  oxy- 
gen and  throw  off  its  waste,  without  the  need  of  a  set  of  organs  for 
carrying  them.  We  do  not  find  a  transportation  system  within 
our  own  home,  nor  even  in  a  small  village,  for  each  individual 
does  his  own  carrying.  In  larger  cities  street  railways  are  neces- 
sary, while  to  care  for  a  whole  state,  numerous  railroads  and  canals 
are  required. 

It  is  the  same  in  animal  structure.  The  simple  forms  have  no 
circulatory  transportation;  in  higher  types  there  are  simple  cir- 
culatory organs  (earthworm) .  In  still  more  complicated  organisms, 
a  heart  and  blood  vessels  are  required  (crayfish),  while  in  the  ver- 
tebrates, especially  birds  and  mammals  with  their  very  highly 
specialized  organs,  there  is  needed  a  very  complete  and  complex 
transportation  system,  in  order  that  each  cell  may  be  supplied. 

Now  we  may  carry  our  comparison  between  cell  functions  and 
life  on  Crusoe's  island  a  step  further  and  find  another  result  of 

392 


CIRCULATION 


393 


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394 


BIOLOGY  FOR  BEGINNERS 


OfAGRAW   OF   CIRCULATION    IN 
MAMMALS 


VEINS 


ARTERIES 


fpulmone 


specialization.  We  will  recall  the  likeness  between  the  one-celled 
protozoan  and  Crusoe.  He  had  to  perform  for  himself  all  the 
functions  of  life,  such  as  preparing  his  food,  making  his  clothes 
and  building  his  home.  The  higher  forms  of  life  are  like  small 

communities  where  one 
man  may  build  the 
houses  or  another  specia- 
lize in  making  clothes. 
This  would  correspond 
to  the  first  steps-  in 
specialization,  as  shown 
by  sponges,  hydra,  etc. 
As  the  communities 
grow,  many  men  work 
together  at  one  trade  to 
supply  all,  and  this 
would  illustrate  the 
grouping  of  specialized 
cells  into  tissues,  each 
performing  its  function 
for  the  whole  animal 
(earth  worm).  Then  in 
larger  communities  the 
wants  are  more  num- 
erous, more  groups  of 
men  specialize  in  dif- 
fent  tato  and  supp.y 
others  at  a  distance  with 
their  products.  This  is  the  stage  represented  by  the  higher  animals, 
where  a  transportation  (circulatory)  system  is  required.  In  man 
this  is  accomplished  by  the  blood,  which  is  kept  in  motion  by  the 
heart,  and  flows  through  arteries,  veins,  and  capillaries. 

The  Blood.  The  blood  is  a  fluid  tissue  constituting  about  T^  of 
the  weight  of  the  body.  It  consists  of  a  liquid  portion,  calle'd  the 
plasma  and  solid  portions,  called  the  corpuscles  or  blood  cells. 
The  plasma  constitutes  f  the  bulk  of  the  blood  and  consists  of 


FIG.  127.    Diagram  showing  circulation  in 


CIRCULATION 


395 


a  liquid  (serum)  which  carries  the  food  and  waste  products,  and  a 
proteid  substance  (fibrinogen),  which  when  exposed  to  air  aids  in 
forming  a  clot  to  stop  bleeding.  The  corpuscles  are  of  two  sorts, 
red  and  white;  the  former  much  more  numerous,  thus  giving 
the  red  color  to  the  blood. 

The  red  corpuscles  are  minute,  disc-shaped,  blood  cells,  so  small 
that  ten  million  can  be  spread  on  a  square  inch,  yet  so  numerous 


FIG.  128.  Blood  corpuscles.  A ,  magnified  about  400  diameters.  The  red 
corpuscles  have  arranged  themselves  in  rouleaux;  a,  a,  colorless  corpuscles; 
B,  red  corpuscles  more  magnified  and  seen  in  focus;  £,  a  red  corpuscle  slightly 
out  of  focus.  Near  the  right  hand  top  corner  is  a  red  corpuscle  seen  in  three- 
quarter  face,  and  at  C  one  seen  edgewise.  F,  G,  H,  I,  white  corpuscles  highly 
magnified.  From  Martin-Fitz. 

that  there  are  enough  in  the  average  body  to  form  a  row  four  times 
around  the  equator.  Their  red  color  is  due  to  a  complex  iron  com- 
pound (haemoglobin)  which  carries  oxygen  from  the  lungs  to  the 
tissues.  When  laden  with  oxygen  it  is  a  bright  red,  but  becomes 
darker  when  the  oxygen  is  removed,  causing  the  difference  in  color 
of  the  blood  on  going  to  and  coming  from  the  tissues. 
The  white  corpuscles  are  really  almost  colorless  and  can  change 


396 


BIOLOGY  FOR  BEGINNERS 


their  shape  much  like  the  amoeba.  There  are  probably  several 
kinds  and  their  functions  differ,  but  seem  to  be  concerned  in  aiding 
the  absorption  of  fats  and  in  destroying  disease  germs  in  the  blood. 
They  are  formed  in  the  lymph  glands.  They  have  the  power  to 
penetrate  the  capillary  walls  and  wander  through  the  lymph  spaces; 
they  collect  at  wounds  and  points  of  infection  and  oppose  the  at- 
tack of  disease  germs. 

Healing  a  Wound.  In  the  healing  of  a  cut  there  are  several  proc- 
esses set  at  work  by  the  blood.  First,  as  the  blood  oozes  out, 
fibrinogen  is  exposed  to  the  air,  hardens  to  fibrin,  entangles  the 
corpuscles,  and  the  clot  or  scab  forms.  Then  the  blood  supply  is 
automatically  increased  to  bring  extra  white  corpuscles  on  guard 
to  oppose  infection;  this  causes  the  redness  (inflammation).  As 
the  fibrin  forms,  it  contracts,  causing  the  puckering  of  a  scar  and 
as  fast  as  new  tissue  is  built,  the  clot  or  scab  is  shed.  A  slight 
scratch  or  blister  often  lets  only  the  plasma  through,  while  a 
"  black  and  blue  "  bruise  is  in  part  due  to  breakage  of  capillary 
walls  and  consequent  clotting  of  blood  under  the  skin. 

Changes  in  Composition  of  Blood.  The  composition  of  the  blood 
is  constantly  changing  as  it  receives  and  distributes  its  various 
burdens.  This  is  shown  in  the  following  table. 

CHANGES  IN  COMPOSITION  OF  BLOOD 


Blood  loses 

Blood  receives 

In  all  active  tissues 

Materials  for  growth,  repair 
and  energy 

Wastes  of  oxidation 
Carbon    dioxide    and 
water 
Nitrogenous  wastes 

In  walls  of  digestive 
organs 

Materials  for  making  digestive 
fluids  and  for  growth,  ac- 
tivity, and  repair  of  the  di- 
gestive organs 

Digested  nutrients 

In  the  lungs 

Carbon  dioxide  and  water 

Oxygen 

In   the  kidneys  and 
skin 

Water  and  urea 

Carbon  dioxide,  etc. 

CIRCULATION  397 

Probably  the  blood  is  actually  purest  when  leaving  the  kidneys, 
though  it  is  still  dark  colored,  due  to  lack  of  oxygen.  It  is  not 
correct  to  speak  of  "  dark  blood  "  as  always  being  "  impure  blood." 

The  Heart.  The  heart  is  a  hollow,  cone-shaped  muscle,  located 
behind  the  breast  bone,  between  the  lungs,  nearly  on  the  center 
line  of  the  body;  the  point  is  downward  and  lies  between  the  fifth 
and  sixth  ribs  a  little  to  the  left.  Since  the  "  beat  "  is  strongest 
near  the  tip  it  has  given  the  idea  that  the  whole  heart  is  on  the  left 
side,  which  is  not  true.  The  heart  consists  of  two  entirely  separate 
halves,  right  and  left,  each  of  which  consists  of  a  thin- walled  auricle 
and  a  thick  muscular  ventricle.  The  auricles  act  as  reservoirs  for 
the  incoming  blood  and  permit  a  steady  flow  and  rapid  filling  of 
the  ventricles.  The  ventricles,  by  alternate  expansion  and  con- 
traction, force  the  blood  into  the  arteries  and  so  around  the  body. 
Between  each  auricle  and  its  ventricle  are  valves  which  allow  blood 
to  enter  the  ventricle  but  prevent  its  exit,  except  by  the  arteries, 
and  at  the  base  of  each  artery  are  valves  preventing  the  blood  from 
flowing  back  into  the  ventricles. 

Action  of  Heart.  The  right  auricle  receives  de-oxygenated  blood 
from  the  veins  through  which  it  has  been  collected  from  the  whole 
body.  This  passes  through  the  valve  into  the  right  ventricle,  which, 
when  it  contracts,  forces  it  to  the  lungs,  via  the  pulmonary  arteries. 
In  the  lungs,  the  blood  receives  a  new  load  of  oxygen,  unloads  some 
carbon  dioxide  and  water,  and  returns  via  the  pulmonary  veins  to 
the  left  auricle.  From  here  it  passes  through  the  valves  into  the 
left  ventricle  and  is  thence  forced  out  through  the  aorta  to  all  parts 
of  the  body.  The  ventricles  contract  and  expand  together  so 
there  are  two  waves  of  blood  sent  out  at  each  beat,  one  to  the  lungs 
and  one  to  the  general  circulation.  While  the  ventricles  are  con- 
tracting and  forcing  out  their  blood,  both  auricles  have  been  filling 
so  there  is  no  stop  in  the  flow. 

Rate  of  Beat.  The  rate  of  heart  beat  is  normally  72  times  per 
minute  in  man;  80,  in  women;  much  higher  in  young  children 
and  in  very  old  persons,  reaching  the  average  at  about  twenty 
years  of  age.  Naturally,  the  amount  of  blood  needed  is  affected 
by  exercise,  temperature,  food,  excitement,  pain,  etc.,  and  so  all 


398  BIOLOGY  FOR  BEGINNERS 

these  automatically  change  the  rate  of  heart  beat.  When  we  run 
upstairs  (a  bad  habit,  by  the  way)  we  use  more  energy,  hence  oxi- 
dize more  tissue,  hence  need  more  oxygen  to  be  brought  by  the 
blood,  and  produce  more  waste,  which  must  be  carried  off,  and  the 
heart  has  to  work  harder  to  meet  this  demand. 

Blood  Vessels.  Arteries.  All  the  vessels  that  carry  blood  away 
from  the  heart  are  arteries  regardless  of  whether  they  carry  red 
(oxygenated)  or  dark  (de-oxygenated)  blood.  Arteries  have  elastic 
muscular  walls,  and  very  smooth  linings.  Their  function  is  to  assist 
and  to  regulate  blood  flow.  Since  they  are  elastic  they  expand 
when  blood  is  forced  into  them,  and  as  the  valves  prevent  it  from 
returning  to  the  heart,  their  elastic  contraction  forces  it  to  flow 
on  through  the  arteries  and  exerts  pressure  clear  to  the  capillaries. 

If  it  were  not  for  this  elasticity,  which  is  greatest  in  the  large 
arteries,  the  circulation  would  be  slow  and  unsteady  and  the  ar- 
teries themselves  in  danger  of  bursting  under  the  sudden  strain, 
when  the  ventricles  contract.  In  "  hardening  of  the  arteries  " 
this  elasticity  is  lost  and  produces  serious  and  usually  fatal 
results. 

In  general  the  arteries  are  protected  by  location  beneath  thick 
muscles,  but  at  the  wrist  and  neck  some  large  ones  come  near  the 
surface  and  this  elastic  wave  of  expansion  can  be  felt,  and  is  known 
as  the  pulse. 

The  muscles  in  the  artery  walls  perform  the  very  important 
function  of  regulating  the  amount  of  blood  that  reaches  a  given 
organ.  By  a  very  complicated  system  of  nerve  control,  these 
muscles  expand  when  more  blood  is  required  and  contract  when  the 
supply  is  not  needed. 

Capillaries.  As  the  arteries  leave  the  heart  they  divide  again 
and  again,  becoming  smaller  and  thinner  walled  till  they  develop 
into  microscopic  tubes  with  a  wall  of  only  one  layer  of  cells.  These 
tiny  blood  vessels  are  the  capillaries  ("  hair  like  ")  and  are  so 
numerous  that  they  reach  every  living  tissue  of  the  body.  Their 
large  area  and  thin  walls  permit  osmosis  to  go  on  readily  and  it  is 
by  way  of  osmosis  from  the  capillaries  that  food  actually  reaches 
the  body  cells.  Absorption  of  food  in  the  digestive  tract  and  ex- 


CIRCULATION 


399 


cretion  of  waste  from  tissues  in  lungs,  skin,  and  kidneys  are  also 
by  way  of  these  very  important  blood  vessels. 


FIG.  129.  The  lymphatic  vessels.  The  thoracic  duct  occupies  the  middle 
of  the  figure.  It  lies  upon  the  spinal  column,  at  the  sides  of  which  are  seen 
portions  of  the  ribs  (1).  a,  the  receptacle  of  the  chyle;  b,  the  trunk  of  the 
thoracic  duct,  opening  at  c  into  the  junction  of  the  left  jugular  (/)  and  sub- 
clavian  (g)  veins  as  they  unite  into  the  left  innominate  vein,  which  has  been 
cut  across  to  show  the  thoracic  duct  running  behind  it;  d,  lymphatic  glands 
placed  in  the  lumbar  regions;  h,  the  superior  vena  cava  formed  by  the  junc- 
tion of  the  right  and  left  innominate  veins.  From  Martin-Fitz. 

Veins.  On  leaving  an  organ  the  capillaries  unite  to  form  veins, 
which  grow  larger  as  they  approach  the  heart,  and  always  carry 


400  BIOLOGY  FOR  BEGINNERS 

blood  toward  this  organ.  Their  walls  are  thinner  than  the  arteries, 
having  little  elastic  or  muscular  tissue,  but  many  of  the  larger  ones 
are  provided  with  cup-like  valves  to  prevent  backward  flow  of 
blood.  Veins  are  often  just  beneath  the  skin  and  can  be  easily 
seen  on  the  back  of  the  hand  where  the  dark  color  of  their  blood  is 
conspicuous;  enlargements  show  the  location  of  the  valves.  Veins 
have  no  pulse  wave  and  the  blood  pressure  is  lower  than  in  the 
arteries.  Except  for  the  pulmonary  veins,  their  blood  is  dark  (de- 
oxygenated)  as  compared  with  the  redder,  arterial  blood.  However, 
this  is  of  little  use  in  deciding  whether  a  wound  has  cut  a  vein  or 
artery,  as  on  exposure  to  ah*,  blood  absorbs  oxygen  and  brightens 
in  color. 

Bleeding  from  an  artery,  if  large  enough  to  be  serious,  is  in 
pulse-like  spurts,  while  the  flow  from  veins  is  steady.  This  and 
the  location  of  the  wound  are  the  best  means  of  distinguishing 
the  source  of  blood  flow. 

Lymph  Circulation.  A  part  of  the  blood  plasma  that  diffuses 
through  the  capillary  walls  into  the  spaces  between  the  cells  does 
not  return  to  the  capillaries  directly  but  is  collected  into  the  lymph 
capillaries. 

These  tiny  tubes  connect  all  the  lymph  spaces  together  and  unite 
to  form  the  lymph  veins  which  eventually  join  to  empty  into  the 
blood  stream  near  the  left  jugular  (neck)  vein.  Thus,  a  part  of  the 
plasma,  instead  of  following  the  usual  route  (artery  —  capillary  — 
vein)  may  return  as  follows,  artery  —  capillary  —  lymph  space 
—  lymph  capillary  —  lymph  vein  —  true  vein.  It  is  in  the  form 
of  this  lymph  that  the  blood  actually  nourishes  the  tissues  and  the 
lymphatic  circulation  is  just  as  necessary  as  that  of  the  blood 
as  a  whole. 

Each  cell  of  the  body  is  practically  an  island  surrounded  by 
lymph.  This  lymph  has  passed,  by  osmosis,  through  the  capillary 
walls,  bearing  in  solution  the  digested  food-stuffs  from  the  ali- 
mentary tract,  and  oxygen  from  the  lungs. 

These  the  cell  uses  in  its  life  activities  and  throws  off  carbon 
dioxide,  water,  and  other  wastes  into  the  lymph,  and  thence  into 
the  blood  of  the  vein  capillaries. 


CIRCULATION  401 

White  corpuscles  may  pass  through  the  walls  of  the  capillaries 
and  thus  get  into  the  lymph  spaces,  from  whence  they  may  pass 
out  with  the  returning  lymph,  by  way  of  the  lymph  capillaries, 
to  rejoin  the  blood,  through  the  lymph  system. 

The  lymph  thus  stands  between  the  blood  stream  in  the  capil- 
laries, and  the  living  cells  of  the  body.  The  blood  leaves  the  heart 


O 

C.       CtRAOH     DtOflDE 

F.         FOOT3      //V   SOLUTION' 

IV.        WASTE       MATTER 

conPusei.es 


FIG.  130.    Diagram  to  show  relation  between  blood,  lymph,  and  cells. 

by  one  route,  the  arteries,  and  returns  part  way  by  two,  namely 
the  veins  and  the  lymph  system.  These  unite  before  reaching  the 
heart  again. 

COLLATERAL   READING 

Civic  Biology,  Hunter,  pp.  313-328;  Studies  "in  Physiology,  Peabody, 
pp.  117-158;  Elementary  Physiology,  Huxley,  pp.  119-147;  Applied 
Physiology,  Overton,  pp.  156-191;  Physiology  for  Beginners,  Foster  and 
Shore,  pp.  78-107;  General  Physiology,  Eddy,  pp.  [159-203;  Physiology 
Textbook,  Colton,  pp.  48-104;  Human  Body  and  Health,  Davison,  pp.  106- 
130;  High  School  Physiology,  Hughes,  pp.  154-178. 

SUMMARY 
Function  of  circulatory  system. 

Transportation  of  food  from  digestive  organs  to  tissues. 
Transportation  of  oxygen  from  lungs  to  tissues. 
Transportation  of  waste  from  tissues  to  lungs  and  kidneys. 
Reasons  for  varying  degrees  of  development. 
Blood. 

Composition.     Plasma:  (two-thirds  bulk). 
Serum,  carrier  of  food  and  waste. 
Fibrinogen,  aids  in  forming  clot. 


402  BIOLOGY  FOR  BEGINNERS 

Corpuscles:  (one-third  bulk). 
Red,  disc-shaped  cells,  minute,  and  numerous,  contain  haemoglobin 

(oxygen  carrier). 
White,  amoeboid,  can  penetrate  tissues,  destroy  germs,  help  absorb 

fats. 
Blood  and  the  healing  of  wounds. 

1.  Fibrinogen  exposed,  fibrin  forms  clot. 

2.  White  corpuscles  brought  by  extra  blood  supply. 

3.  New  tissue  built  and  scar  forms. 

Changes  in  blood  composition.     (See  tabulation  in  text.) 

Heart. 

Shape,  hollow,  cone-shaped  muscle. 

Location,  between  lungs,  behind  breast  bone,  point  to  left. 

Structure. 

Auricles,  thin  walled,  act  as  reservoirs,  cause  steady  flow. 

Ventricles,  thick-walled,  muscular,  propel  the  blood. 
Valves,  at  base  of  arteries  and  between  auricles  and  ventricles,  prevent 

back  flow  of  blood. 
Action. 

De-oxygenated  blood  from  body,  via  caval  veins  flows  to  right  auricle, 
right  ventricle,  pulmonary  artery,  lungs. 

Oxygenated  blood   from  lungs  returns   via  pulmonary  vein  to  left 

auricle,  left  ventricle,  aorta,  general  body  circulation. 
Rate. 

72-80  beats  per  minute. 

Dependent  on  age,  activity,  state  of  mind,  etc. 

Arteries. 

Carry  blood  from  the  heart. 

Structure,  smooth  lining  to  permit  easy  blood  flow. 

Elastic  tissue  to  allow  for  pressure  and  propel  blood. 

Muscular  tissue  to  regulate  blood  supply. 

Deeply  placed  for  protection.     Thick  walled. 

Veins. 

Carry  blood  toward  the  heart. 

Structure,  smooth  lining,  pocket  valves  to  prevent  back  flow. 

Thin  walled,  and  little  elastic  or  muscle  tissue. 

Placed  nearer  the  surface,  no  pulse  wave. 

Capillaries. 

Connect  arteries  and  veins. 

Very  thin,  small,  and  numerous. 

Provide  surface  for  osmosis  in  nutrition,  respiration,  and  excretion. 
Lymph  circulation. 

Function. 

Route. 


CHAPTER  XLI 
EXCRETION 

Vocabulary 

Urine,  the  liquid  excreted  by  the  kidneys. 

Urea,  a  nitrogenous  substance  in  the  urine,  waste. 

Duct,  tube  which  carries  excreted  or  secreted  matter. 

Excretion,  throwing  off  of  waste. 

Secretion,  production  of  useful  substance  by  glands. 

All  the  activities  of  the  body  require  energy,  whether  in  the  mus- 
cles, nerves,  or  glands.  Energy  implies  oxidation,  and  oxidation 
produces  waste  products  which  must  be  removed.  The  main 
wastes  of  the  body  are  carbon  dioxide  and  water  and  nitrogenous 
compounds  (mainly  urea)  together  with  some  mineral  salts,  chiefly 
sodium  chloride  (common  salt). 

Organs  of  Excretion.  The  most  important  organs  of  excretion 
are  the  kidneys  and  lungs;  then  come  the  intestine,  liver,  and  last, 
the  skin  which  has  other  more  important  functions. 

Kidneys.  The  kidneys  are  bean-shaped  glands  located  near  the 
spine  at  the  "  small  of  the  back."  They  are  about  two  by  four 
inches  in  size  and  are  usually  imbedded  in  fat.  Their  internal 
structure  is  too  complicated  for  description  here,  but  is  perfectly 
fitted  for  removing  from  the  blood,  urea,  uric  acid,  other  nitrogen 
compounds,  mineral  salts,  and  water.  Their  blood  supply  is  very 
large  and  under  high  pressure,  which  is  important  in  removal  of 
these  wastes.  As  it  leaves  the  kidneys  in  the  renal  veins,  the  blood 
is  actually  purer  than  anywhere  else  in  the  body  though  it  may  still 
be  dark  in  color,  due  to  lack  of  oxygen. 

The  ducts  from  the  kidneys  lead  to  the  bladder  where  the  urine 
(which  is  constantly  being  excreted)  is  stored.  The  amount  of 
urine  is  usually  about  three  pounds  per  day  and  the  nitrogenous 

403 


404  BIOLOGY  FOR  BEGINNERS 

wastes  which  it  contains  are  of  such  character  that  if  incompletely 
removed,  very  serious  diseases  are  sure  to  result. 

Exposure  to  cold,  drinking  large  quantities  of  water,  and  excess 
of  proteid  food  all  tend  to  increase  the  amount  of  urine.  As  some 
of  the  waste  matters  are  not  very  soluble,  it  is  a  good  thing  to 

* 


FIG.  131.  Section  perpendicularly  through  skin,  a,  epidermis;  b,  pigmentary 
layer  of  epidermis;  c,  papillary  layer  of  dermis;  d,  dermis  or  true  skin;  e,  fatty 
tissue;  /,  g,  h,  sweat  glands  and  duct;  i,  k,  hair  with  its  follicle  and  papilla; 
I,  sebaceous  gland.  (After  Brubaker.)  From  Kellogg. 

drink  plenty  of  water  to  keep  the  kidneys  well  washed  out.    As  a 
rule  we  drink  too  little  rather  than  too  much. 

The  Lungs.  The  lungs  are  used  as  organs  of  excretion  as  well 
as  for  the  supply  of  oxygen,  their  wastes  being  carbon  dioxide 
mainly,  together  with  considerable  water  and  very  little  nitrog- 
enous compounds. 


EXCRETION  405 

The  Liver  and  Intestines.  The  liver  and  intestines  are  both 
concerned  with  the  removal  of  bile,  a  part  of  which  is  waste  matter, 
and  the  intestines  also  remove  the  unused  food  refuse,  which,  how- 
ever is  not  strictly  excretion. 

The  Skin.  The  skin  excretes  considerable  water  and  only  1  per 
cent  of  solid  matter,  mainly  salts,  and  a  very  little  urea.  The 
chief  function  of  perspiration  is  to  regulate  the  temperature  of  the 
body. 

Structure.    While  not  primarily  an  organ  of  excretion,  the  struc- . 
ture  and  functions  of  the  skin  may  be  discussed  at  this  point. 
The  human  skin  is  a  much  thicker  and  more  important  organ  than 
we  usually  suppose.     When  tanned  into  leather  it  resembles  the 
pig-skin  cover  of  a  foot  ball. 

It  consists  of  an  outer  portion  (epidermis)  composed  of  many 
layers  of  cells,  the  outer-most,  dead,  horny  scales,  the  inner  ones, 
more  active  and  larger.  Its  function  is  mainly  protective  and  the 
outer  scales  are  constantly  being  rubbed  off  and  replaced  by  new 
from  beneath.  Where  subject  to  much  friction  or  pressure  the  epi- 
dermis may  grow  to  over  a  hundred  cell  layers  in  thickness,  pro- 
ducing the  familiar  callouses  of  hands  and  feet. 

Hair,  nails,  and  color  cells  are  developed  from  the  epidermal 
layer  in  man.  Scales,  feathers,  and  claws  are  modified  forms  found 
in  other  animals. 

Beneath  the  epidermis  is  a  thicker  layer  (the  dermis)  consist- 
ing of  tough  fibrous  connective  tissue,  richly  supplied  with  blood 
and  lymph  vessels,  nerves,  sweat,  and  oil  glands. 

Functions  of  the  Skin.    These  include: 

1.  Protection  from  germ  attack  and  mechanical  injury. 

2.  Protection  of  inner  tissues  from  drying.    The  skin,  aided  by 
the  oil  glands,  is  nearly  water  proof,  neither  absorbing  nor  letting 
out  moisture,  except  at  the  sweat  pores. 

3.  It  is  the  location  of  most  of  our  nerves  of  touch. 

4.  Excretion  of  sweat  as  a  waste  matter. 

5.  Excretion  of  sweat  to  regulate  the  temperature  of  the  body. 
This  last  statement  needs  explanation.     Birds  and  mammals 

are  the  only  animals  whose  temperature  does  not  change  with 


406  BIOLOGY  FOR  BEGINNERS 

that  of  their  surroundings.  The  rate  of  oxidation  and  hence  the 
production  of  heat  varies  even  more  than  the  outside  temperature 
and  this  means  that  a  heat-regulating  device  is  required. 

Heat  is  required  to  evaporate  water;  therefore  if  moisture  is 
excreted  on  the  surface  of  the  skin,  the  body's  heat  is  taken  up  in 
evaporating  it  and  consequently  the  skin  is  cooled.  The  blood 
supply  to  the  skin  is  great,  the  surface  exposed  for  evaporation  is 
also  large,  and  so  by  the  use  of  the  body  heat  to  vaporize  (dry  off) 
the  perspiration,  the  blood,  and  hence  the  whole  body,  is  cooled. 

The  greater  our  activity  or  the  warmer  the  surrounding  air, 
the  larger  is  the  amount  of  perspiration,  and  hence  the  greater 
cooling  effect. 

A  complex  system  of  nerve  control  .governs  the  blood  supply 
and  gland  activity  of  the  skin,  so  that,  mainly  by  its  means  our 
temperature  is  kept  at  98.5  degrees.  The  importance  of  this  func- 
tion of  the  skin  is  seen  when  we  realize  that  a  temperature  of  8  or 
10  degrees  either  above  or  below  the  normal  is  usually  fatal. 

COLLATERAL   READING 

Physiology  Textbook,  Colton,  p.  381;  General  Physiology,  Eddy,  pp. 
352-373;  Applied  Physiology,  Overtoil,  pp.  248-255;  Human  Mechansim, 
Hough  and  Sedgwick,  pp.  177-186;  Human  Body  and  Health,  Davison, 
pp.  175-190;  Studies  in  Physiology,  Peabody,  pp.  232-252;  Human  Body, 
Martin,  pp.  215-229;  Elementary  Physiology,  Huxley,  pp.  193-247;  High 
School  Physiology,  Hughes,  pp.  197-213. 

SUMMARY 

Waste,  source,  oxidation  in  tissues. 

Kind,  carbon  dioxide,  water,  nitrogenous  compounds,  salts. 
Organs  of  excretion. 

1.  Kidneys,  location,  small  of  back,  near  spine. 

Size,  two  by  four  inches,  bean  shaped. 

Blood  supply  large,  high  pressure. 

Ducts  connecting  with  bladder. 

Remove  water,  urea,  salts,  etc.  (3  Ib.  daily). 

2.  Lungs. 

Remove  carbon  dioxide,  water,  little  nitrogenous  waste. 

3.  Liver  and  intestines. 

Remove  bile  and  unused  food  stuff. 


EXCRETION  407 

4.   Skin. 

Removes  water,  salts,  etc.     (Not  primarily  excretory.) 
Structure. 

Epidermis,  scale-like  cells,  loose. 

Protective,  callouses. 

Modified  as  hair,  nails,  claws,  horns,  etc. 
Dermis,  fibrous  cells. 

Many  blood  and  lymph  capillaries. 

Nerves,  sweat  and  oil  glands. 
Functions. 

Protection  from  germs. 

Protection  from  injury. 

Protection  from  drying  of  tissues. 

Protection  from  water. 

Sensation. 

Excretion. 

Temperature  regulation. 

Sweat  excreted. 

Evaporated  by  body  heat. 

Body  therefore  cooled. 


CHAPTER  XLII 
THE  NERVOUS  SYSTEM 

Vocabulary 

Convolutions,  irregular  grooves  in  the  surface  of  the  cerebrum. 

Voluntary,  under  control  of  the  will. 

Harmonize,  to  coordinate,  to  make  to  work  together. 

The  brain  is  the  one  organ  which  in  man  is  capable  of  greater 
development  than  any  other  animal.  No  amount  of  training  will 
enable  us  to  compete  with  the  fish,  bird,  dog,  or  snake  in  speed, 
strength,  locomotion,  or  keenness  of  sense.  Practically  every 
animal  excels  man  in  some  way  and  the  one  thing  that  makes 
man  their  superior  is  his  greater  intelligence,  which  means  greater 
brain  development. 

Despite  this,  we  often  devote  more  attention  to  other  lines,  in 
which  we  cannot  hope  for  really  useful  success,  and  leave  to  very 
indifferent  care  the  training  of  our  one  source  of  superiority. 

While  we  cannot  deal  with  the  structure  of  the  brain  in  detail, 
the  need  of  some  controlling  organ  to  regulate  the  complicated 
functions  of  any  animal's  body  is  very  apparent  and  we  must 
needs  take  up  its  study,  if  only  very  briefly. 

Structure.  The  brain  consists  of  three  general  regions,  the 
cerebrum,  the  cerebellum,  and  the  spinal  bulb.  Connected  with  it 
are  the  spinal  cord  and  nerves  which  together  with  the  brain  com- 
pose the  central  nervous  system. 

Cerebrum.  The  cerebrum  constitutes  about  nine-tenths  of  the 
brain;  it  occupies  the  upper  part  of  the  skull  and  is  divided  into 
two  halves  or  hemispheres.  Its  surface  is  deeply  folded  in  ir- 
regular grooves  (convolutions)  and  consists  of  gray  nerve  cells, 
while  internally  the  bulk  of  its  tissue  is  made  up  of  white  nerve 
fibers. 

408 


THE  NERVOUS   SYSTEM 


409 


The  vastly  complex  structure  by  which  each  cell  is  cross  con- 
nected to  thousands  of  others,  the 
tree-like  branching  of  the  nerves,  the 
grouping  in  larger  fibers  and  passage 
from  one  part  to  another  of  the  brain 
and  spinal  cord,  all  will  have  to  be 
omitted.  We  know  that  it  is  the 
most  complicated  organ  in  the  world 
but  we  are  far  from  a  complete 
understanding  of  its  structure,  much 
less  its'  mode  of  operation. 

Experiment  and  disease  have 
shown  that  the  cerebrum  is  the 
center  of  intelligence,  thought, 
memory,  will,  and  the  emotions. 
It  is  the  region  of  conscious  sensa- 
tion, by  which  we  perceive  all  that 
goes  on  about  us,  and  in  it  arise 
the  impulses  which  produce  all  our 
voluntary  motions. 

Cerebellum.  The  cerebellum  is 
situated  behind  and  below  the  cere- 
brum, is  much  smaller,  is  not  divi- 
ded, and  has  shallower  and  more 
regular  convolutions.  Its  function  is 
mainly  to  regulate  and  harmonize 
(coordinate)  muscular  action.  This 
is  very  essential.  When  we  run,  or  FIG.  132.  Central  organs  of  the 
skate,  or  walk,  or  swim,  or  throw  a  nervous  system.  F,  TO,  frontal, 

temporal  and  occipital  lobes  of  the 

ball,  we  use  nearly  all  of  the  five  cerebrum;  C,  cerebellum;  p.pons 
hundred     muscles     of     our     body,    varolii;    mo,  medulla   oblongata; 

Each  muscle  fiber  is  controlled  by  a  n^~ms:  upper  and  lower  limits  of 

*        the  spinal  cord;  CVII,  8th  cervical 
nerve;    each    nerve    impulse    must  nerve;  DXII>  12th  dorsal  nerve. 

reach  its  muscle  at  the  proper  in-    (Quain   after  Bourgery.)     From 

stant.    When  we  stop  to  analyze  the  Kell°gg- 

simplest  act  and  think  how  many  muscles  are  made  to  work  to- 


410  BIOLOGY  FOR  BEGINNERS 

gether  in  perfect  harmony,  we  realize  how  important  is  this  co- 
ordination of  muscular  action  by  the  cerebellum.  Without  it, 
though  the  cerebrum  might  originate  the  impulse  to  do  a  certain 
act,  no  regulated  useful  motion  could  result. 

Medulla.  The  spinal  bulb  (medulla)  is  really  an  enlargement  of 
the  spinal  cord  but  is  within  the  skull  and  closely  attached  to  the 
cerebellum.  It  is  about  the  size  of  a  walnut  and  is  located  at  the 
extreme  base  of  the  brain. 

The  spinal  bulb  is  the  center  of  control  of  respiration,  circula- 
tion, secretion,  movements  of  digestive  organs  and  of  swallowing, 
as  well  as  other  similar  automatic  and  unconscious  activities. 
Naturally,  death  follows  injury  to  this  vitally  important  part  of 
the  brain,  though  severe  damage  to  the  other  parts  may  not  be 
fatal. 

Spinal  Cord.  The  spinal  cord  extends  from  the  medulla  through 
the  protective  bony  arch  of  each  vertebra,  down  almost  the  whole 
length  of  the  spine,  and  from  it  branch  the  nerves  that  supply  all 
parts  of  the  body,  except  those  which  spring  from  the  brain  directly. 
The  spinal  cord  is  not  merely  a  large  nerve  trunk,  however,  but  is 
the  center  of  many  involuntary  muscular  actions  (reflex  actions) 
of  the  body  and  limbs.  If  we  touch  a  hot  stove,  we  do  not  have  to 
think  to  remove  our  hands.  If  something  comes  near  an  eye,  we 
do  not  have  to  depend  on  the  brain  to  close  the  eye.  Voluntary 
action  would  take  too  long  and  injury  would  result  before  the  brain 
could  have  time  to  act,  so  all  such  reflex  actions  are  centered  in  the 
spinal  cord  and  operate  automatically  but  not  unconsciously  as  do 
the  motions  of  the  internal  organs  controlled  by  the  medulla. 

The  spinal  cord,  then,  has  two  functions: 

(1)  A  connecting  trunk  between  brain  and  other  nerves. 

(2)  The  center  of  reflex  action. 

Sympathetic  System.  On  each  side  of  the  spinal  column  but 
inside  the  body  cavity  are  two  rows  of  nerve  ganglia  which  are 
connected  with  each  other  and  with  the  brain  and  spinal 
cord. 

From  this  double  nerve  chain  extend  branches  to  most  of  the 
internal  organs  and  to  other  ganglia  located  in  the  chest  and  ab- 


THE  NERVOUS  SYSTEM 


411 


domen.  The  largest  of  these  sympathetic  ganglia  is  the  solar 
plexus,  located  just  below  the  diaphragm,  another  is  near  the  heart, 
and  a  third  low  down  in  the  abdomen. 

The  operation  of  the  sympathetic  system  is  not  well  understood 
but  it  certainly  controls  the  secretion  of  glands,  the  regulation  of 
blood  supply  in  arteries,  heart  action,  and  probably  many  other 
internal  activities  of  which  we  are  not  conscious,  but  without  which 
we  could  not  live. 

The  "  sympathetic  system  "  has  nothing  to  do  with  "  sympathy  " 


BRAIN  -  (MID-SECTION) 

FIG.  133.     Diagram  of  mid-section  of  human  brain  showing  position  of 
important  parts. 

in  its  usual  sense,  but  is  so  named  since  it  seems  to  keep  the  in- 
voluntary internal  organs  working  in  harmony,  much  as  the  cerebel- 
lum coordinates  the  action  of  the  voluntary  organs. 

It  appears  that  our  nervous  system  is  capable  of  controlling 
several  kinds  of  action,  for  example: 

1.  Voluntary  actions,  originating  in  the  cerebrum  and  co- 
ordinated by  cerebellum. 


412  BIOLOGY  FOR  BEGINNERS 

2.  Involuntary  and  unconscious  action  of  internal  organs  con- 
trolled by  medulla  and  sympathetic  system. 

3.  Involuntary  but  conscious  reflex  actions  controlled  by  the 
spinal  cord. 

4.  Actions,  at  first  voluntary,  that  have  become  reflex  (auto- 
matic) by  habit,  like  learning  to  walk. 

Habit  Formation.  To  accomplish  a  given  act  or  thought,  the 
nerve  impulse  has  to  connect  up  various  parts  of  the  brain.  At 
first  this  is  done  with  difficulty  and  we  say  we  are  "  learning  to 
read  "  or  to  ride  a  bicycle  or  play  a  piano.  However,  repeated 
voluntary  acts  soon  make  their  proper  nerve  connections  easier,, 
as  if  a  path  were  being  worn  in  the  brain  along  which  the  impulses 
travel  with  greater  and  greater  ease. 

If  we  continue  doing  a  certain  act  or  thinking  a  certain  way  often 
enough,  it  becomes  the  easiest  way  to  act  or  to  think,  and  we  say 
we  have  "  acquired  the  habit."  If  we  look  up  the  derivation  of 
that  word,  habit,  we  find  that  it  comes  from  "  habeo,"  meaning  to 
have  or  hold.  So  instead  of  our  getting  the  habit,  as  we  say,  the 
habit  has  "  got  "us. 

It  is  a  serious  thing  to  think  of,  for  our  whole  life  is  a  complex 
mass  of  habits,  —  things  which  hold  us,  —  acts  and  thoughts  that 
do  themselves,  and  which  we  "  just  can't  help."  How  careful  we 
should  be  that  those  brain  paths  are  the  best  arranged  so  that 
habits  of  thought  shall  be  prompt  and  accurate.  How  watchful 
we  should  be  that  only  good  and  helpful  paths  be  followed,  for, 
whether  we  wish  it  or  not,  the  habit  will  get  and  hold  us.  It  is  only 
too  true  that  "  As  a  man  thinketh  .  .  .  so  is  he." 

"  The  hell  to  be  endured  hereafter,  of  which  theology  tells,  is 
no  worse  than  the  hell  we  make  for  ourselves  in  this  world  by 
habitually  fashioning  our  characters  in  the  wrong  way.  Could 
the  young  but  realize  how  soon  they  will  become  mere  walking 
bundles  of  habits,  they  would  give  more  heed  to  their  conduct 
while  in  the  plastic  state.  We  are  spinning  our  own  fates,  good  or 
evil,  and  never  to  be  undone.  Every  smallest  stroke  of  virtue  or 
of  vice  leaves  its  never-so-little  scar.  The  drunken  Rip  Van  Winkle, 
in  Jefferson's  play,  excuses  himself  for  every  fresh  dereliction  by 


THE  NERVOUS  SYSTEM  413 

saying, '  I  won't  count  this  time! '  Well!  he  may  not  count  it,  and 
a  kind  Heaven  may  not  count  it;  but  it  is  being  counted  none  the 
less.  Down  among  his  nerve  cells  and  fibers  the  molecules  are 
counting  it,  registering  and  storing  it  up  to  be  used  against  him 
when  the  next  temptation  comes.  Nothing  we  ever  do  is,  in  strict 
scientific  literalness,  wiped  out.  Of  course  this  has  its  good  side 
as  well  as  its  bad  one.  As  we  become  permanent  drunkards  by  so 
many  separate  drinks,  so  we  become  saints  in  the  moral,  and  au- 
thorities in  the  practical  and  scientific,  spheres  by  so  many  separate 
acts  and  hours  of  work.  Let  no  youth  have  any  anxiety  about 
the  upshot  of  his  education,  whatever  the  line  of  it  may  be.  If 
he  keep  faithfully  busy  each  hour  of  the  working  day,  he  may  safely 
leave  the  final  result  to  itself.  He  can  with  perfect  certainty  count 
on  waking  up  some  fine  morning,  to  find  himself  one  of  the  com- 
petent ones  of  his  generation,  in  whatever  pursuit  he  may  have 
singled  out."  —  James,  Psychology. 

COLLATERAL   READING 

Physiology  Textbook,  Colton,  pp.  254-298;  General  Physiology,  Eddy, 
pp.  382-428;  Applied  Physiology,  Overton,  pp.  266-275;  Human  Mecha- 
nism, Hough  and  Sedgwick,  pp.  266-288;  Human  Body  and  Health,  Davi- 
son,  pp.  215-236;  Studies  in  Physiology,  Peabody,  pp.  253-290;  Human 
Body,  Martin,  pp.  230-262;  Elementary  .  Physiology,  Huxley,  pp.  475- 
551;  High  School  Physiology,  Hughes,  pp.  214-234. 

SUMMARY 

Reason  for  Special  Training  of  the  Brain. 
General  Function,  Control. 
Parts  of  Nervous  System. 

1.  Brain. 

Cerebrum,  location,  size,  shape,  surface,  character  of  substance. 

Functions,   intelligence,    will,    thought,    sensation,    voluntary 

motion. 
Cerebellum,  location,  size,  surface. 

Function,  muscular  coordination,  for  voluntary  acts. 
Medulla  (spinal  bulb),  location,  size. 

Function,  control  of  respiration,  circulation,  etc. 

2.  Spinal  cord,  location  (cf.  spinal  column). 

Functions,  nerve  connection. 
Reflex  control. 


414 


BIOLOGY  FOR  BEGINNERS 


3.  Nerves,  to  receive  sensation,  and  transmit  motion  impulses. 

4.  Sympathetic  system,  location. 

Structure,  plexuses  (solar,  cardiac,  abdominal). 
Function,  coordinates  involuntary  actions. 


Nervous  system  controls 

by  means  of 

examples 

1.  Voluntary  actions 

2.  Involuntary    actions    (un- 
conscious) 
3.  Involuntary     reflex     (con- 
scious) 
4.  Automatic  actions 

Cerebrum 
Cerebellum 
Medulla 
Sympathetic  system 
Spinal  cord 

Whole  system 

CHAPTER  XLIII 

THE  SENSE  ORGANS 

Vocabulary 

Irritability,  response  of  simple  organs  to  environment. 
Papillae,  minute  projections  supplied  with  nerve  endings. 
Pigment,  color  substance. 
Concentrate,  to  bring  to  one  point,  to  focus. 
Competent,  able. 

The  chief  function  of  the  nervous  system  mentioned  in  the  pre- 
vious chapter  was  that  of  control.  It  has  another  equally  im- 
portant use,  namely  to  keep  us  in  touch  with  our  surroundings  by 
what  we  call  sensation. 

Irritability.  All  living  things  respond  more  or  less  to  their  en- 
vironment. Plants  react  to  light,  moisture,  contact,  and  gravita- 
tion, and  thus  have  a  very  simple  sort  of  sensation,  usually  called 
"  irritability."  These  responses  are  sufficient  for  their  needs,  as 
our  experiments  have  shown,  and  enable  plants  to  reach  food  and 
water  supplies,  to  turn  leaves  toward  light,  to  climb  by  means  of 
tendrils  and  to  perform  certain  movements  concerned  in  pollena- 
tion  and  seed  dispersal. 

Touch.  Even  the  simplest  animals  are  affected  by  actual  con- 
tact with  surroundings.  The  amceba  recoils  from  hard  or  hot 
particles,  absorbs  food  when  in  contact  with  it,  and  thus  may  be 
said  to  exhibit  a  primitive  sense  of  touch. 

In  higher  forms,  the  whole  body  surface  possesses  this  sense 
more  or  less.  It  is  often  especially  developed  in  tentacles,  hairs, 
or  papillae  in  various  animals.  In  man  the  sense  of  touch  is  com- 
mon to  all  parts  of  the  skin,  especially  the  finger  tips,  forehead,  and 
tongue.  The  human  skin  also  possesses  special  nerves  that  receive 
temperature,  pressure,  and  pain  sensations.  If  we  gently  touch 

415 


416  BIOLOGY  FOR  BEGINNERS 

different  places  on  the  back  of  the  hand  with  a  pencil  point,  some 
spots  will  feel  warm  and  others  cold,  due  to  the  presence  or  absence 
of  these  temperature  nerves. 

Taste.  All  animals  seem  to  prefer  some  foods  and  reject  others. 
We  have  to  assume  a  sort  of  taste  sense  to  account  for  this.  To  be 
tasted,  a  substance  has  to  be  in  solution  and  in  contact  with  certain 
organs  near  the  mouth.  The  mouth  parts,  palpi  and  tongue  are 
the  usual  taste  organs,  and  in  man  the  different  parts  of  the  tongue 
are  sensitive  to  different  tastes.  The  back  part  responds  only  to 
bitter,  the  tip  to  sweet,  the  sides  to  sour,  and  the  whole  surface  to 
salty  flavors.  Much  that  we  attribute  to  taste  is  really  due  to  the 
sense  of  smell;  if  eyes  and  nose  are  closed  one  can  hardly  dis- 
tinguish between  an  apple,  onion,  or  raw  potato.  Taste  enables 
animals  to  judge  of  foods,  stimulates  the  flow  of  digestive  fluids, 
and  in  aquatic  forms  may  give  information  as  to  their  location 
in  the  water. 

Smell.  Both  touch  and  taste  require  the  substance  to  be  in 
actual  contact  if  it  is  perceived.  Smell  reaches  a  little  farther 
away  and  enables  animals  to  detect  substances  in  the  form  of 
vapor  or  dilute  solution,  even  though  at  a  distance. 

The  organs  of  smell  are  sometimes  hairs,  often  antennae,  while 
vertebrates  have  some  sort  of  a  "  nose."  They  are  usually  near 
the  food-getting  organs,  and  in  air  breathers,  are  associated  with 
the  inlet  to  the  lungs.  Primarily  the  sense  of  smell  is  used  to  judge 
of  food  and  air  supply  but  in  many  cases  it  is  also  useful  in  finding 
food,  detecting  enemies,  and  locating  mates.  It  is  little  developed 
in  aquatic  animals  but  very  keen  in  insects,  carnivora,  and  most 
ungulates. 

Hearing.  In  contrast  to  the  three  senses  mentioned  above, 
hearing  puts  us  in  touch  with  our  surroundings  through  the  me- 
dium of  sound  waves  conveyed  by  air  or  water.  This  brings  within 
range  of  our  consciousness  things  at  a  much  greater  distance  and 
is  the  chief  avenue  of  communication  among  all  higher  animals, 
most  of  which  possess  some  form  of  sound-producing  organs. 

The  simplest  ears  in  worms,  molluscs,  and  crustaceans  consist 
of  mere  sacs  lined  with  nerve  endings.  In  insects  the  sacs  are 


THE  SENSE  ORGANS 


417 


covered  with  a  tympanum  or  drum  membrane,  and  possibly  the 
antennae  are  sensitive  to  sound  vibrations  as  well.  Ear  organs 
may  be  located  on  legs,  abdomen,  antennae,  and  head  in  various 
animals. 

Structure  of  the  Human  Ear.    The  vertebrate  ear  is  a  wonder- 
fully complicated  organ,  consisting  of  an  external  ear  which  opens 


Auditory 
nerve 


FIG.  134. 


Basilar  membrane 


Eustachian  tube 


Semi-diagrammatic  section  through  the  right  ear. 
(After  Martin.)     From  Kellogg. 


into  an  auditory  canal  embedded  in  the  skull.  This  canal  is  closed 
at  its  inner  end  by  the  tympanic  membrane,  which  separates  it 
from  the  middle  ear. 

The  middle  ear  connects  with  the  throat  by  way  of  the  eusta- 
chian  tube  which  serves  to  equalize  the  air  pressure  on  both  sides 
of  the  drum  and  thus  prevents  breakage,  while  permitting  free 
vibration.  Across  the  middle  ear  extends  a  chain  of  tiny  bones 
which  connects  the  tympanic  membrane  with  a  somewhat  similar 
membrane  in  the  wall  of  the  inner  ear. 

The  internal  ear  consists  of  two  general  parts.  The  cochlea  is  a 
cavity  in  the  skull  shaped  like  a  snail  shell,  filled  with  a  liquid  and 


418  BIOLOGY    FOR  BEGINNERS 

lined  with  a  complicated  set  of  nerve  endings,  which  receive  the 
sound  impressions.  The  semicircular  canals,  three  in  number,  are 
little  loop-shaped  tubes  each  at  right  angles  to  the  other,  and 
have  to  do  with  maintaining  the  balance  of  the  body. 

How  We  Hear.  When  a  person  speaks  to  you,  he  starts  certain 
air  waves  which  are  gathered  in  by  the  external  ear,  and  conveyed 
to  the  tympanum,  which  is  thus  made  to  vibrate.  By  means  of  the 
bones  of  the  middle  ear,  this  vibration  is  communicated  to  the 
fluid  in  the  inner  ear,  and  this  in  turn  acts  upon  the  nerve  endings 
of  the  cochlea.  This  disturbance  of  the  nerve  endings  is  trans- 
mitted to  the  brain  by  way  of  the  auditory  nerves  and  we  hear  the 
sound  of  words. 

The  human  ear  can  distinguish  vibrations  varying  from  sixteen 
to  forty  thousand  per  second,  but  we  have  reason  to  believe  that 
insects  can  hear  sounds  of  higher  pitch. 

Care  of  the  Ears.  Fortunately  this  delicate  and  important 
organ  is  deeply  imbedded  in  the  skull  where  little  harm  can  reach 
it,  but  care  must  be  observed  not  to  injure  the  tympanum  by 
probing  with  hard  implements,  ear  spoons,  etc.,  when  trying  to 
clean  the  ear.  In  this  connection  it  has  been  said  that  one  ought 
never  to  explore  their  ears  with  anything  sharper  than  their  elbow. 

Ear  wax  has  a  useful  function  in  keeping  out  dirt  and  insects, 
and  excess  can  be  properly  removed  by  ordinary  washing.  Foreign 
bodies  should  be  washed  out  and  never  removed  by  "  poking  " 
with  hairpins  and  other  implements.  Water  which  .enters  the 
ears  in  diving  does  no  harm,  and  can  easily  be  shaken  out. 

Ear  ache  or  a  discharge  from  the  ear  may  indicate  a  serious  con- 
dition and  should  have  immediate  attention  from  a  physician. 
The  brain  and  ear  cavities  are  very  close  together  at  one  point, 
so  that  inflammation  of  the  ear  may  reach  the  brain  with  fatal 
results. 

.  Temporary  deafness  may  be  caused  by  inflammation  of  the 
eustachian  tubes  as  a  result  of  a  cold.  Permanent  deafness  may 
be  caused  by  a  blow  on  the  ear  bursting  the  tympanum,  or  by 
disease  of  the  middle  or  inner  ear.  It  is  always  a  serious  matter 
and  should  never  be  treated  by  advertising  quack  doctors,  whose 


THE  SENSE  ORGANS  419 

only  skill  consists  in  their  ability  to  separate  their  victims  from 
their  money. 

Sight.  Plants  and  the  lower  animals  respond  to  light  but  can 
hardly  be  said  to  "  see."  The  sensation  of  sight  reaches  us  by 
way  of  waves  in  the  ether,  which  are  studied  more  fully  in  Physics. 
These  light  waves  reach  us  from  vast  distances  and  at  enormous 
speed  and  put  us  in  touch  with  a  wider  extent  of  our  surroundings 
than  all  the  other  senses  combined.  This  fact,  and  its  relation  to  our 
other  activities,  make  sight  the  most  valued  of  all  our  senses.  Yet 
there  is  hardly  an  organ  that  we  abuse  more  than  we  do  our  eyes. 

The  simplest  eyes  were  mere  colored  spots  connected  with  special 
nerves  to  absorb  light  and  tell  its  direction.  Now  we  have  lenses 
developed  to  concentrate  light  upon  these  sensitive  pigment  spots, 
muscles  to  adjust  both  lens  and  eye  and  various  devices  to  protect 
the  whole. 

Structure  of  the  Human  Eye.  The  eye  is  almost  spherical  in 
shape,  flattened  a  little  from  front  to  rear.  The  wall  of  the  eye- 
ball consists  of  three  layers.  The  outer  one  is  tough  and  white, 
called  the  sclerotic  coat,  and  shows  in  front  as  the  "  white  of  the 
eye."  The  anterior  surface  of  the  sclerotic  bulges  out  a  little,  and 
becomes  transparent  in  the  circular  region  called  the  cornea. 

The  second  coat,  called  the  choroid,  is  richly  supplied  with 
blood  vessels  and  pigment  (color)  cells  which  prevent  reflection  of 
light  inside  the  eye-ball.  This  coat  shows  in  front  as  the  iris  or 
"  color  "  of  the  eye.  The  iris  is  provided  with  muscles  which  regu- 
late the  size  of  the  center  opening,  the  pupil,  according  to  the 
amount  of  light. 

The  inner  layer  is  the  most  delicate  and  complicated  part  of  the 
eye  and  is  called  the  retina.  It  is  really  the  expanded  end  of  the 
optic  nerve  and  connects  directly  with  the  brain.  It  also  has  a  dark 
pigment  and  though  only  ¥V  of  an  inch  in  thickness,  it  consists 
of  at  least  seven  distinct  layers  of  cells  which  help  in  receiving  the 
impression  which  we  call  sight. 

The  lens  of  the  eye  is  located  just  behind  the  iris  and  is  con- 
nected to  the  choroid  by  delicate  muscles  which  can  change  its 
thickness,  to  adjust  for  near  or  distant  vision. 


420 


BIOLOGY  FOR  BEGINNERS 


PLATE 


S  H  O  r  T  E  H 


A  wo  rwe 

FIG.  135. 


The  space  in  front  between  the  lens  and  cornea  is  filled  with 
a  watery  fluid  and  the  ball  of  the  eye  is  occupied  by  a  jelly-like, 
transparent  substance,  which  keeps  the  eye  in  shape. 

How  We  See.  Light  waves  from  an  object  pass  through  the 
cornea  to  the  lens  which  concentrates  (focuses)  them  upon  the 


THE  SENSE  ORGANS  421 

retina  as  you  would  focus  a  picture  on  the  film  of  your  camera. 
The  iris  controls  the  amount  of  light  entering  the  eye  and  the  lens 
muscles  change  its  shape  so  that  the  picture  on  the  retina  may  be 
sharp  and  clear.  The  retina  is  affected  by  the  light  that  falls 
upon  it  and  the  impression  is  carried  to  the  brain  by  the  optic 
nerve,  as  sight. 

Protection  of  the  Eye.  Obviously,  the  eye  cannot  be  buried  in 
the  skull  for  protection,  like  the  ear,  but  it  is  well  guarded  none  the 
less.  The  bony  socket,  walled  in  by  the  forehead,  nose  and  cheek 
ward  off  any  but  direct  blows.  The  pad  of  fat  on  which  it  rests 
saves  it  from  jar  or  pressure.  The  eyebrows  keep  out  perspiration 
and  the  lids  and  lashes  protect  from  dust.  Tear  secretion  con- 
stantly washes  the  front  surface  and  a  complicated  set  of  reflex 
actions  helps  us  to  ward  off  most  injuries  to  this  important  sense 
organ. 

The  Living  Camera.  The  eye  is  often  compared  to  a  camera 
and  there  are  so  many  resemblances,  that  it  may  be  helpful  to 
study  this  table  of  comparisons. 

Part  of  eye          corresponding  to         Part  of  Camera 

Ball  Camera  box 

Lens  Lens 

Lids  Shutter 

Iris  Stops  or  diaphragm 

Pupil  Lens  opening 

Lens  muscles  Focusing  devices 

Black  pigment  Black  lining 

Retina  Plate  or  film 


In  making  this  comparison  it  must  always  be  borne  in  mind  that 
there  are  also  fundamental  differences.  The  eye  is  alive,  the  camera 
is  not.  The  eye  produces  a  sensation  which  reaches  the  brain,  the 
camera  makes  a  picture.  The  eye  focuses  by  changing  the 
shape  of  the  lens,  the  camera,  by  changing  its  distance  from  the 
film. 


422 


BIOLOGY  FOR  BEGINNERS 


Defects  of  the  Eye.  The  care  of  the  eye  is  dealt  with  in  the 
chapter  on  hygiene,  but  it  is  well  to  remember  that  seldom  are  they 
perfectly  normal  and  frequent  examination  by  a  competent  physi- 
cian is  the  only  sure  way  of  preserving  their  health.  Below  are 
tabulated  some  of  the  common  conditions  and  their  causes,  but 
only  an  expert  can  determine  the  exact  kind  of  lens  or  method  of 
treatment  which  will  remedy  the  defect. 


Condition 

Defect  of  eye 

Remedy 

Near  sight 
Far  sight 
Astigmatism 

Old  age 

Eye  ball  too  long 
Eye  ball  too  short 
Irregularity  in  shape  of  lens, 
or  cornea 
Loss  of  lens  adjustment  result- 
ing in  far  sight 

Concave  lens  glasses 
Convex  lens  glasses 
Special  cylinder  lens  glasses 

Convex  lens  glasses 

COLLATERAL   READING 

Animal  Studies,  Jordan,  Kellogg  and  Heath,  pp.  371-386;  Animal 
Life,  Jordan  and  Kellogg,  pp.  224-239;  Physiology  Textbook,  Colton,  pp. 
284-300;  General  Physiology,  Eddy,  pp.  436-485;  Applied  Physiology, 
Overton,  pp.  268-275;  The  Human  Mechanism,  Hough  and  Sedgwick,  pp. 
244-265;  The  Human  Body  and  Health,  Davison,  pp.  237-258;  Studies 
in  Physiology,  Peabody,  pp.  291-320;  The  Human  Body,  Martin,  pp. 
263-294;  Elementary  Physiology,  Huxley,5  pp.  367-457;  High  School 
Physiology,  Hughes,  pp.  239-260. 


SUMMARY 


Response  to  environment. 

1.  Irritability. 

2.  Touch. 

3.  Taste. 

4.  Smell. 

5.  Hearing 


(a)  Structure  of  ear. 

Outer  ear,  auditory  canal  and  lobe. 
Middle  ear,  bones,  eustachian  tube. 
Inner  ear,  cochlea  and  nerve  endings,  semicircular  canals. 


THE  SENSE  ORGANS 


423 


Exampl 


£  a  §%    Us ^ 

|g££    §!H 


.B 

c 


s  a"  a" 


S 


424  BIOLOGY  FOR  BEGINNERS 

(£>)  How  we  hear, 
(c)   Care  of  ears. 

6.   Sight. 

(a)  Structure  of  eyes. 
Coats, 

Sclerotic,  white,  thick,  protective,  cornea  in  front. 
Choroid,  blood  vessels  and  pigment,  iris  in  front. 
Retina,  dark,  complicated,  receives  impressions. 
Lens,  convex,  adjustable  by  muscles. 
(&)  How  we  see. 

(c)  Protection  of  the  eye. 

(d)  The  living  camera. 

(e)  Defects  of  the  eye. 


CHAPTER  XLIV 
BIOLOGY  AND  HEALTH 

Vocabulary 

Excessive,  more  than  necessary. 
Mastication,  chewing. 
Flexible,  easily  bent. 
Vagaries,  whims. 

One  of  the  chief  reasons  for  the  study  of  biology  is  to  learn  how 
to  properly  care  for  our  own  body  and  to  maintain  both  it  and  its 
surroundings  in  healthful  condition. 

The  science  which  deals  with  the  care  and  health  of  the  body  is 
called  hygiene;  that  which  deals  with  keeping  its  environment 
healthful  is  called  sanitation. 

A  great  many  foolish  "  rules  of  hygiene  "  have  been  devised  but 
if  we  will  apply  our  general  knowledge  of  biology,  mixed  with  a 
goodly  amount  of  common  sense  (which  is  not  common),  we  can 
construct  our  own.  We  know  the  amount  and  kinds  of  foods  re- 
quired, and  can  judge  the  evils  of  improper  or  excessive  eating. 
We  know  the  need  and  process  of  digestion  and  can  reach  our  own 
conclusion  as  to  chewing  food,  care  of  teeth,  removal  of  waste,  etc. 

We  have  learned  the  use  of  oxidation  and  can  see  the  reason  for 
correct  posture,  clothing,  and  exercise,  which  affect  breathing. 
In  this  way  a  sensible  human  being  ought  to  be  able  to  apply  bi- 
ology to  his  own  life  and  it  is  much  better  than  trying  to  memorize 
any  set  of  rules,  however  wise  they  may  be. 

In  the  same  way,  sanitation  means  the  knowledge  of  biology 
as  applied  to  food  and  water  supply,  infectious  diseases,  ventila- 
tion, sewerage,  clean  streets,  etc. 

In  our  elementary  work  we  have  studied  both  these  subjects  to 
some  extent.  This  chapter  will. merely  attempt  to  summarize  a 
few  of  the  principal  facts. 

425 


426  BIOLOGY  FOR  BEGINNERS 

Health  is  the  natural  condition  of  the  body,  and  yet,  how  many 
have  never  been  sick,  or  are  now  in  absolutely  perfect  health.  We 
must  remember  that  any  lack  of  health  is  due  to  some  biologic 
mistake.  While  we  can  probably  never  know  enough  to  absolutely 
avoid  disease  certainly  our  study  of  biology  ought  to  help  us  to 
escape  those  troubles  whose  causes  we  do  know.  If  we  lived  as 
well  as  we  knew  how,  everybody  would  be  much  stronger,  healthier, 
and  happier.  It  is  to  call  attention  to  some  of  the  simpler  ap- 
plications of  biology  to  health,  that  this  chapter  is  written. 

Hygiene  of  the  Muscles.  A  great  deal  is  being  done  with  re- 
gard to  proper  muscular  exercise  and  it  is  well  to  understand  some 
of  the  reasons  for  the  importance  of  this  matter.  The  least  impor- 
tant result  is  one  most  often  mentioned,  namely  the  fact  that  ex- 
ercises strengthen  the  muscles  used.  This  is  true  but  the  following 
results  are  much  more  important  to  health. 

1.  Exercise  increases  oxidation,  from  three  to  ten  times;  this 
means  that  greater  bodily  energy  is  liberated. 

2.  From  this  it  follows  that  the  heat-regulating  and  excretory 
organs  are  trained  to  their  work. 

3.  Exercise  withdraws  the  blood  from  the  internal  organs,  to  the 
muscles  and  so  relieves  the  tendency  to  over-supply  and  conges- 
tion; this  is  shown  by  the  "  healthy  color  "  of  the  complexion  due 
to  the  blood  supply  in  the  outer  muscles;  a  very  pale  skin  usually 
indicates  poor  health. 

4.  Only  by  proper  exercise  do  the  heart  and  arteries  receive 
necessary  training  in  supplying  the  blood  to  the  tissues. 

5.  In  the  same  way,  exercise  aids  in  the  use  and  health  of  the 
lungs  and  breathing  organs. 

6.  Motion  of  the  muscles  is  one  of  the  chief  causes  of  lymph 
flow  and  we  know  that  upon  the  lymph  circulation  depends  the 
nutrition  of  the  tissues. 

No  rules  can  be  given  as  to  special  kinds  of  exercise,  since  dif- 
ferent people  need  different  forms,  just  as  we  need  different  amounts 
of  food,  but  in  general  it  may  be  said  that  any  exercise  should 
bring  about  the  results  mentioned  above,  and  should  not  be  such 
as  to  endanger  or  overstrain  any  part  of  the  body. 


BIOLOGY  AND   HEALTH 


427 


Proper  exercise  should 

1.  Be  vigorous,  continuous,  and  reasonably  prolonged.     For 


FIG.  136.  Superficial  muscles  of  trunk,  shoulder  and  back  viewed  from 
behind.  A,  external  occipital  protuberance;  1-1,  trapezius  muscles;  l'  oval 
tendon  between  right  and  left  trapezius;  l'  insertion  of  trapezius;  B,  summit 
of  shoulder  (acronium);  2-2',  lateral  muscle  and  insertion;  3,  sterno-mastoid; 
4,  deltoid;  5,  infraspinatus;  6,  teres  minor;  7,  teres  major;  8,  rhomboideus 
major;  9,  part  of  external  oblique  muscle  of  abdomen.  (After  Allen  Thom- 
son.) From  Kellogg. 

example  a  brisk  walk  is  one  of  the  best  of  exercises,  while  a  short 
stroll  or  saunter  does  little  good,  though  often  mistaken  for  "  ex- 
ercise." 


428  BIOLOGY  FOR  BEGINNERS 

2.  Useful  exercise  should  use  the  body  muscles  as  well  as  arms  and 
legs:  walking,  swimming,  and  throwing  are  good  examples. 

3.  Exercise  should  cause  full,  deep  breathing  and  preferably 
should  be  in  the  open  air.    Loose  clothing  and  erect  position  neces- 
sarily follow. 

4.  Exercise  should  be  varied  and  should  occupy  the  mind  as 
well  as  the  body;   any  movements,  however  excellent,  lose  much 
if  they  are  not  enjoyed  while  being  performed.    This  is  the  objec- 
tion to  many  really  beneficial  "  systems  of  exercise  "  which  become 
very  distasteful  because  of  lack  of  interest. 

Hygiene  of  Digestion.    For  the  general  study  of  foods  refer  to 
Chapter  37.    The  following  is  a  summary  of  facts  explained  there: 

1.  The  amount  and  kind  of  food  should  be  adjusted  to  the  work 
of  the  body. 

2.  The  "  balance  "  of  the  ration  should  be  maintained. 

3.  The  food  should  be  clean  and  properly  prepared. 

4.  Usually  the  heartiest  meal  should  come  after  the  day's  work 
and  should  be  preceded  by  a  brief  rest.    Only  when  the  brain  or 
muscles  are  not  working,  can  the  digestive  organs  get  proper  supply 
of  blood. 

5.  Eating  between  meals  is  usually  a  bad  practice,  especially 
in  case  of  sweet  foods,  as  it  prevents  proper  desire  for,  and  diges- 
tion of,  the  solid  food  which  the  body  requires. 

6.  Water  in  abundance  should  be  used  both  between  and  at 
meals,  but  not  to  "  wash  down  "  unchewed  food.     It  does  not 
"  dilute  the  gastric  fluid"  but  passes  quickly  from  the  stomach 
and  digestion  is  aided  rather  than  hindered. 

7.  It  is  unnecessary  to  dwell  upon  the  importance  of  thorough 
chewing.    The  smaller  the  food  particles,  the  greater  the  surface 
exposed  for  digestion  and  the  less  burden  is  put  upon  the  stomach. 
The  starch  digestion  in  the  mouth  may  not  be  very  extensive,  but 
thorough  mastication  prevents  over-eating  and  too  rapid  eating, 
both  of  which  produce  more  indigestion  than  all  other  causes  put 
together.     "  Leave  the  table  hungry  "  is  a  good  rule.     Americans 
eat  too  much,  particularly  of  proteid  foods,  a  habit  which  is  both 
unhealthful  and  expensive. 


BIOLOGY  AND  HEALTH  429 

8.  Proper  care  of  the  teeth  is  necessary  if  food  is  to  be  thoroughly 
chewed.    It  is  sufficient  to  remember  that  tooth  decay  is  a  bac- 
terial process,  that  the  warmth  and  moisture  of  the  mouth  make 
ideal  conditions  for  bacterial  growth,  and  that  perfect  cleanliness  is 
our  only  means  of  protection.     This  suggests  frequent  careful 
brushing,  use  of  antiseptic  tooth  washes,  and  a  visit  to  a  dentist 
at  least  twice  a  year  "  whether  you  need  it  or  not." 

9.  Violent  exercise,   severe   study,   worry,   or  any   mental  or 
physical   activity,  at  or  near  meal-times  interferes  with  proper 
digestion. 

10.  Regular  attention  must  be  given  to  the  removal  of  waste 
from  the  intestine,  as  a  long  series  of  illnesses  can  be  traced  to 
lack  of  care  in  this  regard. 

Hygiene  of  Respiration.  We  have  learned  the  use  which  the  body 
makes  of  oxygen  in  releasing  the  energy  in  our  foods  and  keeping 
us  alive  and  active.  Naturally,  proper  breathing  is  required  if  this 
process  is  to  go  on  in  a  healthful  way. 

We  need  to  train  our  breathing  muscles,  because  few  of  us  know 
how  to  breathe,  even  though  we  use  the  expression  "  natural  as 
breathing." 

Deep  breathing  means  using  more  lung  tissue,  getting  more 
oxygen,  and  developing  the  diaphragm  and  rib  muscles, 
properly. 

We  cannot  use  all  our  lung  capacity  at  once,  but  should  use  all 
we  can.  We  train  the  other  muscles  for  less  important  uses;  why 
not  train  our  breathing  muscles  for  the  race  of  life? 

Erect  position  and  comfortable  clothing  are  necessary  if  we  are 
to  breathe  properly. 

The  nose  was  made  for  breathing,  not  the  mouth  (see  Chap.  39) 
and  any  disease  or  growth  which  interferes  with  nose  breathing 
should  be  removed. 

Ventilation.  Deep  breathing  will  do  little  good  if  the  air  breathed 
is  bad:  this  means  attention  to  ventilation.  Proper  ventilation 
should  secure 

1.  A  sufficient  amount  of  air  in  proportion  to  the  number 
concerned 


430  BIOLOGY  FOR  BEGINNERS 

2.  A  slight  continuous  movement  of  air  through  the  whole 
room,  without  perceptible  draughts. 

3.  A  sufficient  degree  of  heat  to  keep  the  body  in  comfort,  usu- 
ally 68  to  70  degrees. 

4.  A  moderate  amount  of  moisture  in  the  air  so  that  it  will 
neither  interfere  with  evaporation  from  the  skin,  nor  yet  tend  to 
dry  it. 

5.  The  removal  of  chemical  impurities  and  odors;   the  amount 
of  CO 2  should  not  exceed  .06  per  cent. 

6.  The  removal  of  excess  moisture  which  is  especially  great  in 
crowded  rooms. 

"  Fresh  air  "  is  not  necessarily  cold  air  as  some  people  seem  to 
think,  though  for  sleeping  rooms,  the  temperature  should  be 
lower  than  in  living  quarters.  Extreme  cold  is  not  an  advantage 
even  in  sleeping  rooms,  except  in  cases  of  tuberculosis,  and  many 
people  subject  themselves  to  dangerous  exposure  in  this  way. 
Air  should  be  pure,  cool,  and  abundant,  but  there  is  no  virtue  in 
extreme  coldness. 

Dust  Removal.  Dust  carries  bacteria,  hence  air  should  be  as 
free  from  it  as  possible.  This  means  replacing  the  broom  and 
feather  duster  by  the  vacuum  cleaner  and  oiled  dust  cloth.  Rugs 
and  hard- wood  floors  should  take  the  place  of  the  permanent  carpet. 
Smooth  walls,  simple  furniture,  and  few  hangings  offer  less  oppor- 
tunity for  the  accumulation  of  dust.  Sprinkling,  oiling,  and 
flushing  the  streets  attain  the  same  result  for  out-door  dust. 

Hygiene  of  the  Eyes.  The  human  eye  is  such  a  delicate  and 
necessary  structure  that  its  care  should  be  emphasized,  but  just 
because  it  is  so  complicated,  no  rules  can  be  made  which  will 
properly  safeguard  this  most  valuable  sense  organ.  The  one  safe 
procedure  is  to  have  the  eyes  examined  by  a  competent  expert 
from  time  to  time,  even  if  no  defect  appears  to  be  developing. 

Reading  in  poor  light,  or  at  evening  when  the  light  is  gradually 
failing,  is  a  common  error.  Almost  as  bad  is  the  use  of  too  bright 
light  directly  facing  the  eyes,  or  reflected  from  too  shiny  paper  in 
books.  Long  continued  use  of  the  eyes  on  very  fine  print  or  sew- 
ing causes  severe  strain,  just  as  in  continued  use  of  any  other  organ. 


BIOLOGY  AND  HEALTH  431 

Actual  defects  in  structure  or,  more  often,  over  use  under  poor 
conditions,  produce  "  eye  strain  "  and  from  this  result  headache, 
sleeplessness,  and  nervous  troubles  of  serious  nature,  in  addition 
to  the  damage  to  the  eye  itself.  Common  sense  in  their  use,  im- 
mediate rest  when  any  feeling  of  fatigue  is  caused,  and  prompt 
advice  from  an  expert,  are  the  only  rules  for  the  care  of  our 
eyes. 

Hygiene  of  Bathing.  Washing  is  primarily  to  remove  dirt.  Dirt 
is  objectionable  for  two  reasons:  it  is  offensive  to  refined  people 
and  it  often  carries  disease  germs. 

Washing  to  "  keep  the  pores  open  "  is  not  a  true  reason,  because 
the  skin  excretes  but  little  waste,  and  the  pores  open  quickly,  even 
in  the  dirtiest  skin,  when  perspiration  is  required  for  heat  regula- 
tion. 

However,  there  is  a  stronger  argument  for  a  daily  cold  bath, 
because  it  gives  the  skin  practice  in  adjusting  itself  to  sudden 
changes  of  temperature  similar  to  those  it  encounters  in  every  day 
exposure.  The  cold  shower  or  sponge  bath,  if  followed  by  brisk 
rubbing,  causes  the  skin  arteries  to  contract,  and  then  expand 
again,  as  evidenced  by  the  glow  of  the  skin. 

This  is  precisely  what  the  body  should  do  when  exposed  to  sud- 
den chill  of  any  sort,  and  if  trained  by  frequent  cold  bathing,  the 
arteries  will  be  ready  to  regulate  the  blood  supply  and  no  cold 
or  congestion  will  result. 

Neither  cold  bathing  nor  swimming  should  be  done  within  at 
least  an  hour  after  meals,  as  the  blood  is  needed  to  absorb  the 
food,  and  should  not  be  diverted  to  the  skin.  The  bath  should 
not  be  so  cold,  nor  the  swim  so  long  continued,  as  to  cause  a  per- 
manent chill  or  prevent  the  warm  reaction  when  the  body  is  rubbed 
dry. 

The  cold  bath  is  primarily  a  means  of  prevention  of  "  colds  " 
and  all  that  they  lead  to;  it  should  be  taken  daily  in  the  morning, 
immediately  upon  rising.  The  warm  bath  is  solely  a  means  of 
cleansing  the  skin,  should  not  be  taken  every  day  and  only  just 
before  retiring,  when  precautions  to  prevent  chill  can  be  observed. 
A  very  hot  bath  should  be  taken  only  by  physician's  orders. 


432  BIOLOGY  FOR  BEGINNERS 

Hygiene  of  the  Teeth.  The  importance  of  dental  hygiene  has 
been  mentioned  before  but  cannot  be  too  much  emphasized. 
Conditions  in  the  mouth  are  ideal  for  the  growth  of  bacteria  which 
cause  decay.  Warmth  and  moisture  are  sure  to  be  present,  and 
unless  great  care  is  observed,  particles  of  food  will  remain  for  the 
bacteria  to  feed  upon. 

It  is  not  a  pleasant  experiment,  but  if  the  teeth  be  scraped  with 
the  finger  nail  and  the  odor  of  the  substance  removed  observed, 
we  will  have  no  doubt  that  decay  is  going  on.  The  total  area  of 
possible  tooth  infection  is  equal  to  that  of  two  standard  petri 
dishes  (over  twelve  square  inches). 

The  decay  of  food  between  the  teeth  destroys  the  protective 
enamel  and  the  dentine  then  goes  rapidly.  The  immediate  re- 
sults are  bad  breath,  pain,  and  loss  of  teeth.  Fully  as  serious  are 
the  secondary  consequences  of  poor  chewing:  indigestion,  pus 
diseases  from  infected  gums,  rheumatism,  and  nervous  disorders. 
Tonsils,  throat,  ears,  and  even  the  lungs  may  be  infected  from  the 
teeth. 

The  first  or  "  milk  teeth  "  deserve  as  great  care  as  the  permanent 
set.  If  they  decay  and  are  removed  too  soon  the  jaws  and  face 
never  attain  their  proper  shape  and  proportion,  and  the  later  teeth 
will  not  fit  properly  together. 

Hygiene  of  the  Feet.  With  the  possible  exception  of  the  eye, 
no  human  organ  has  been  worse  abused  than  the  foot.  We  crowd 
our  feet  into  air-tight  leather  boxes,  bend  the  toes  together,  lift  the 
heel  high  off  the  ground  and  then  wonder  why  we  suffer  from 
corns,  bunions,  and  fallen  arches.  Proper  shoes  should  have  their 
inner  edges  nearly  straight,  heel  low  and  broad,  toe  with  room 
enough  so  that  the  toes  can  separate  and  "  wiggle."  The  uppers 
should  be  flexible,  as  porous  as  possible,  and  not  too  tightly  laced. 
The  arch  of  a  normal  bare  foot  should  not  touch  the  floor  on  the 
inner  edge  and  the  shoe  should  be  so  shaped  as  to  support  this  up- 
ward curve.  The  selection  of  shoes  should  be  guided  by  the  ex- 
pert advice  of  a  doctor  or  trained  fitter  and  not  be  governed  by  the 
vagaries  of  style  or  the  demands  of  fashion.  Feet  were  made  to 
walk  on,  not  to  look  at.  In  walking  the  feet  should  be  carried 


BIOLOGY  AND  HEALTH  433 

forward  with  the  toes  straight  ahead,  not  turned  out  as  is  commonly 
done.  "  Toeing  out  "  is  as  abnormal  as  "  toeing  in  "  but  is  so 
common  that  it  is  less  noticed. 

Posture.  Standing.  The  human  animal  is  not  as  yet  completely 
adapted  to  his  erect  position.  This  makes  especial  care  necessary 
to  achieve  a  healthful  posture  both  in  walking  and  sitting. 

The  head  should  be  held  up  in  a  natural  position  with  chin  drawn 
back,  not  stiffly,  but  with  the  feeling  that  you  are  pushing  your 
hat  up.  The  shoulders  may  be  either  sloping  or  square  by  nature, 
but  need  never  be  rounded  forward.  If  we  still  walked  on  all  fours 
they  would  be  pushed  back  by  our  weight;  now  we  reverse  the 
process  and  carry  weight  upon  them.  This  makes  it  especially 
needful  that  we  hold  our  shoulders  back  and  our  chest  up  to  give 
proper  play  to  the  lungs. 

The  abdominal  organs  tend  to  press  each  other  down  and  for- 
ward. This  has  to  be  met,  partly  by  raising  the  chest  and  partly 
by  strengthening  the  front  body  walls,  to  hold  them  in  place. 

Sitting.  In  our  modern  life  we  do  so  much  work  sitting  down, 
especially  reading  and  writing,  that  particular  care  has  to  be  ex- 
ercised in  regard  to  this.  The  shoulders  are  apt  to  be  bent  forward, 
the  spine  twisted  sidewise,  and  the  weight  brought  too  high  up  by 
sliding  down  in  the  chair.  All  these  habits  cramp  the  breathing 
and  digestive  organs  and  may  produce  permanent  deformity  or 
bad  health.  The  obvious  remedy  is  to  sit  back  in  the  chair,  with 
shoulders  up,  and  lean  forward  only  from  the  hips. 

Hygiene  of  the  Nerves.  Man  has  reached  the  stage  where  mental 
activity  takes  the  place  of  physical  exertion  and  there  is  consequent 
danger  of  one-sided  development. 

Mental  fatigue  is  just  as  real  as  muscular  fatigue.  The  brain 
should  not  be  forced  to  work  when  it  is  already  tired  nor  when  the 
energy  of  the  body  has  been  used  in  hard  physical  labor. 

Mental  hygiene  is  just  as  important  as  physical  hygiene.  A  well- 
trained  brain,  developed  by  proper  exercise,  is  vastly  more  valuable 
than  powerful  muscles  and  needs  even  greater  care  in  its  develop- 
ment. True  education  means  just  this  training  and  developing  of 
a  skillful  brain,  rather  than  merely  storing  the  mind  with  various 


434  BIOLOGY  FOR  BEGINNERS 

kinds  of  information.  Accumulation  of  facts  is  a  very  important 
function  of  the  brain,  it  is  true,  but  is  not  to  be  compared  with  de- 
veloping it  to  observe,  think,  and  really  reason. 

Sleep  is  the  period  of  rest  from  nerve  activity,  relaxation  of 
muscles,  repair  of  waste,  and  growth  of  new  tissue.  Because  chil- 
dren are  growing  as  well  as  using  tissue  by  their  intense  activity, 
they  need  more  sleep  than  the  adult.  While  seven  to  nine  hours 
sleep  will  do  for  most  grown-ups,  children  ought  to  have  from  ten 
to  twelve  hours. 

The  following  are  rules  of  individual  hygiene  as  summarized 
from  the  Yale  Lectures  on  Hygiene  by  Professor  Irving  Fisher. 

Air.    Keep  outdoors  as  much  as  possible. 

Breathe  through  the  nose,  not  through  the  mouth. 

When  indoors,  have  the  air  as  fresh  as  possible  — 

(a)  By  having  aired  the  room  before  occupancy. 

(b)  By  having  it  continuously  ventilated  while  occupied. 
Not  only  purity,  but  coolness,  dryness,  and  motion  of  the  air 

if  not  very  extreme,  are  advantageous.  Air  in  heated  houses  in 
winter  is  usually  too  dry,  and  many  be  humidified  with  advantage. 

Clothing  should  be  sufficient  to  keep  one  warm.  The  minimum 
that  will  secure  this  result  is  the  best.  The  more  porous  your 
clothes,  the  more  the  skin  is  educated  to  perform  its  functions  with 
increasingly  less  need  for  protection.  Take  an  air  bath  as  often 
and  as  long  as  possible. 

Water.  Take  a  daily  water  bath,  not  only  for  cleanliness,  but  for 
skin  gymnastics.  A  cold  bath  is  better  for  this  purpose  than  a  hot 
bath.  A  short  hot  followed  by  a  short  cold  bath  is  still  better. 
In  fatigue,  a  very  hot  bath  lasting  only  half  a  minute  is  good. 

A  neutral  bath,  beginning  at  97°  or  98°,  dropping  not  more  than 
5°,  and  continued  15  minutes  or  more  is  an  excellent  means  of  rest- 
ing the  nerves. 

Be  sure  that  the  water  you  drink  is  free  from  dangerous  germs 
and  impurities.  "  Soft  "  water  is  better  than  "  hard  "  water. 
Ice  water  should  be  avoided  unless  sipped  and  warmed  in  the 
mouth.  Ice  may  contain  spores  of  germs  even  when  germs  them- 
selves are  killed  by  cold. 


BIOLOGY  AND  HEALTH  435 

Cool  water  drinking,  including  especially  a  glass  half  an  hour 
before  breakfast  and  on  retiring,  is  a  remedy  for  constipation. 

Food.  Teeth  should  be  brushed  thoroughly  several  times  a  day, 
and  floss  silk  used  between  the  teeth.  Persistence  in  keeping  the 
mouth  clean  is  not  only  good  for  the  teeth,  but  for  the  stomach. 

Masticate  all  food  up  to  the  point  of  involuntary  swallowing, 
with  the  attention  on  the  taste,  not  on  the  mastication.  Food 
should  simply  be  chewed  and  relished,  with  no  thought  of  swallow- 
ing. There  should  be  no  more  effort  to  prevent  than  to  force  swal- 
lowing. It  will  be  found  that  if  you  attend  only  to  the  agreeable 
task  of  extracting  the  flavors  of  your  food,  Nature  will  take  care 
of  the  swallowing,  and  this  will  become,  like  breathing,  involuntary. 
The  more  you  rely  on  instinct,  the  more  normal,  stronger,  and  surer 
the  instinct  becomes.  The  instinct  by  which  most  people  eat  is 
perverted  through  the  "  hurry  habit "  and  the  use  of  abnormal 
foods.  Thorough  mastication  takes  time,  and  therefore  one  must 
not  feel  hurried  at  meals  if  the  best  results  are  to  be  secured. 

Sip  liquids,  except  water,  and  mix  with  saliva  as  though  they 
were  solids. 

The  stopping  point  for  eating  should  be  at  the  earliest  moment 
when  one  is  really  satisfied. 

The. frequency  of  meals  and  time  to  take  them  should  be  so 
adjusted  that  no  meal  is  taken  before  a  previous  meal  is  well  out 
of  the  way,  in  order  that  the  stomach  may  have  had  time  to  rest 
and  prepare  new  juices.  Normal  appetite  is  a  good  guide  in  this 
respect.  One's  best  sleep  is  on  an  empty  stomach.  Food  puts 
one  to  sleep  by  diverting  blood  from  the  head,  but  disturbs  sleep 
later.  Water,  however,  or  even  fruit  may  be  taken  before  retiring 
without  injury. 

An  exclusive  diet  is  usually  unsafe.  Even  foods  which  are  not 
ideally  the  best  are  probably  needed  when  no  better  are  available, 
or  when  the  appetite  especially  calls  for  them. 

The  following  is  a  very  tentative  list  of  foods  in  the  order  of 
excellence  for  general  purposes,  subject,  of  course,  to  their  pal- 
atability  at  the  time  eaten:  fruits,  nuts,  grains  (including  bread), 
butter,  buttermilk,  salt  in  small  quantities,  cream,  milk,  potatoes, 


436  BIOLOGY  FOR  BEGINNERS 

and  other  vegetables  (if  fiber  is  rejected),  eggs,  custards,  digested 
cheese  (such  as  cottage  cheese,  cream  cheeses,  pineapple  cheese, 
Swiss  cheese,  Cheddar  cheese,  etc.),  curds,  whey,  vegetables,  if 
fiber  is  swallowed,  sugar,  chocolate,  and  cocoa,  putrefactive  cheeses 
(such  as  Limburger,  Rochefort,  etc.),  fish,  shellfish,  game,  poultry, 
meats,  liver,  sweetbreads,  meat  soups,  beef  tea,  bouillon,  meat 
extracts,  tea  and  coffee,  condiments  (other  than  salt),  and  alcohol. 
None  of  these  should  be  absolutely  excluded,  unless  it  be  the  last 
half  dozen,  which,  with  tobacco,  are  best  dispensed  with  for  reasons 
of  health.  Instead  of  excluding  specific  food,  it  is  safer  to  follow 
appetite,  merely  giving  the  benefit  of  the  doubt  between  two  foods, 
equally  palatable,  to  the  one  higher  in  the  list.  In  general,  hard 
and  dry  foods  are  preferable  to  soft  and  wet  foods.  Use  some  raw 
foods  —  nuts,  fruits,  salads,  milk,  or  other  —  daily. 

The  amount  of  proteid  required  is  much  less  than  ordinarily 
consumed.  Through  thorough  mastication  the  amount  of  proteid 
is  automatically  reduced  to  its  proper  level. 

The  sudden  or  artificial  reduction  in  proteid  to  the  ideal  standard 
is  apt  to  produce  temporarily  a  "  sour  stomach,"  unless  fats  be 
used  abundantly. 

To  balance  each  meal  is  of  the  utmost  importance.  When  one  can 
trust  the  appetite,  it  is  an  almost  infallible  method  of  balancing, 
but  some  knowledge  of  foods  will  help.  The  aim,  however,  should 
always  be  —  and  this  cannot  be  too  often  repeated  —  to  educate 
the  appetite  to  the  point  of  deciding  all  these  questions  auto- 
matically. 

Exercise  and  Rest.  The  hygienic  life  should  have  a  proper 
balance  between  rest  and  exercise  of  various  kinds,  physical  and 
mental.  Generally  every  muscle  in  the  body  should  be  exercised 
daily. 

Muscular  exercise  should  hold  the  attention,  and  call  into  play 
will  power.  Exercise  should  be  enjoyed  as  play,  not  endured  as 
work. 

The  most  beneficial  exercises  are  those  which  stimulate  the 
action  of  the  heart  and  lungs,  such  as  rapid  walking,  running,  hill 
climbing,  and  swimming. 


BIOLOGY  AND  HEALTH  437 

The  exercise  of  the  abdominal  muscles  is  the  most  important 
in  order  to  give  tone  to  those  muscles  and  thus  aid  the  portal  cir- 
culation. For  the  same  reason  erect  posture,  not  only  in  standing, 
but  in  sitting,  is  important.  Support  the  hollow  of  the  back  by  a 
cushion  or  otherwise. 

Exercise  should  always  be  limited  by  fatigue,  which  brings  with 
it  fatigue  poisons.  This  is  nature's  signal  when  to  rest.  If  one's 
use  of  diet  and  air  is  proper,  the  fatigue  point  will  be  much  further 
off  than  otherwise. 

One  should  learn  to  relax  when  not  in  activity.  The  habit  pro- 
duces rest,  even  between  exertions  very  close  together,  and  enables 
one  to  continue  to  repeat  those  exertions  for  a  much  longer  time 
than  otherwise.  The  habit  of  lying  down  when  tired  is  a  good  one. 

The  same  principles  apply  to  mental  rest.  Avoid  worry,  anger, 
fear,  excitement,  hate,  jealousy,  grief,  and  all  depressing  or  ab- 
normal mental  states.  This  is  to  be  done  not  so  much  by  repressing 
these  feelings  as  by  dropping  or  ignoring  them  —  that  is,  by  divert- 
ing and  controlling  the  attention.  The  secret  of  mental  hygiene 
lies  in  the  direction  of  attention.  One's  mental  attitude,  from  a 
hygienic  standpoint,  ought  to  be  optimistic  and  serene,  and  this 
attitude  should  be  striven  for  not  only  in  order  to  produce  health, 
but  as  an  end  in  itself,  for  which,  in  fact,  even  health  is  properly 
sought.  In  addition,  the  individual  should,  of  course,  avoid  in- 
fection, poisons,  and  other  dangers. 

Occasional  physical  examination  by  a  competent  medical  ex- 
aminer is  advisable.  In  case  of  illness,  competent  medical  treat- 
ment should  be  sought. 

Finally,  the  duty  of  the  individual  does  not  end  with  personal 
hygiene.  He  should  take  part  in  the  movements  to  secure  better 
public  hygiene  in  city,  state,  and  nation.  He  has  a  selfish  as  well 
as  an  altruistic  motive  to  do  this.  His  air,  water,  and  food  depend 
on  health  legislation  and  administration. 

COLLATERAL   READING 

School  Hygiene,  Shaw,  entire;  Outlines  of  Practical  Sanitation,  Bashore, 
see  index;  The  Health  of  the  City,  Godfrey,  see  index;  Handbook  of  Health, 


438  BIOLOGY  FOR  BEGINNERS 

Hutchinson,  entire;  Preventable  Diseases,  Hutchinson,  entire;  Civics  and 
Health,  Allen,  see  index;  Primer  of  Sanitation,  Ritchie,  entire;  Good 
Health,  Jewett,  entire;  Mind  and  Work,  Gulick,  entire;  The  Human  Body 
and  Health,  Davison,  see  index;  The  Human  Mechanism,  Hough  and  Sedg- 
wick,  pp.  289-540;  General  Hygiene,  Overton,  see  index;  Practical  Biology, 
Smallwood,  pp.  233-258;  Applied  Biology,  Bigelow,  pp.  525-560. 

SUMMARY 

Hygiene,  care  and  health  of  body  (exercise,  breathing,  food,  eyes,  etc.) 
Sanitation,    providing   healthful   surroundings    (water   supply,    drainage, 
infection,  ventilation). 

1.  Hygiene  of  muscles. 

Exercise,  increases  oxidation. 

Trains  heat  regulating  and  excretion. 

Prevents  internal  congestion. 

Trains  heart  and  arteries. 

Trains  breathing  organs. 

Aids  lymph  circulation. 

Exercise   should   be  vigorous,   use  body  muscles,   cause   deep 
breathing,  occupy  mind. 

2.  Hygiene  of  digestion. 

Food  should  be 

(1)  Adapted  to  body  needs. 

(2)  Balanced  ration. 

(3)  Clean  and  well  prepared. 

(4)  Eaten  when  rested. 

(5)  Eaten  at  regular  times. 

(6)  Accompanied  by  water. 

(7)  Thoroughly  chewed.       . 
Errors  affecting  digestion. 

(1)  Rapid  eating. 

(2)  Insufficient  chewing. 

(3)  Washing  down  food. 

(4)  Eating  too  much. 

(5)  Not  getting  rid  of  waste. 
Care  of  teeth. 

(1)  Frequent  cleaning. 

(2)  Use  of  tooth  wash  or  powder. 

(3)  Consult  dentist  often. 

3.  Respiration. 

(1)  Train  your  breathing  muscles,  ribs  and  diaphragm. 

(2)  Loose  clothing  for  free  action. 

(3)  Erect  position  to  allow  lung  action. 

(4)  Pure  air  supply;  not  necessarily  cold. 

(5)  Air  free  from  dust. 


BIOLOGY  AND  HEALTH  439 

4.  Ventilation. 

Essentials  for  proper  ventilation. 
Dust  removal. 

5.  Care  of  the  eyes. 

Have  frequent  examinations. 

Provide  proper  light,  not  too  bright. 

Avoid  shiny  papers. 

Avoid  continued  severe  use,  producing  fatigue. 

Avoid  reading  in  failing  evening  light. 

Serious  troubles  follow  abuse  of  eyes. 

6.  Hygiene  of  bathing. 

Hot  baths  for  decency  and  cleanliness 

not  to  ""open  the  pores  " 

not  too  frequently 

best  at  bed  time  to  avoid  chilling 
Cold  baths  to  train  body  against  chilling 

should  be  followed  by  rubbing  and  "glow  " 

best  taken  in  morning 

not  too  cold  nor  too  prolonged. 

7.  Care  of  the  teeth. 

Conditions  in  mouth  favor  bacterial  growth. 

Harm  to  teeth  from  bacteria,  decay  and  loss. 

Other  damage  to  health  and  looks,  due  to  poor  teeth. 

8.  Hygiene  of  the  feet. 

Danger  from  improper  shoes. 
Shape  and  material  of  shoes. 
Correct  habits  of  walking. 
Support  of  the  arches  of  the  feet. 

9.  Correct  posture. 

Standing  position. 
Sitting  position. 

10.   Hygiene  of  the  nervous  system. 

Great  development  of  nervous  system. 

Possibility  of  over  strain  and  neglect  of  rest  of  body. 

Importance  of  well-trained  brain. 

Importance  of  sleep. 


CHAPTER  XLV 
CIVIC  BIOLOGY 

Vocabulary 

Pessimism,  looking  on  the  "dark  side"  of  things. 

Civic,  pertaining  to  government. 

Prolific,  abundant. 

Conservation,  saving  from  waste  or  damage. 

Addiction,  the  grip  of  habit. 

The  preceding  chapter  has  dealt  mainly  with  biology  as  related 
to  the  individual,  but  more  important  is  our  duty  to  the  health  of 
the  community,  state,  and  nation. 

Out  of  two  and  one-half  million  babies  born  in  the  United  States 
every  year,  one  half  die  before  reaching  the  age  of  twenty- three 
years,  and  500,000  die  before  their  first  birthday.  Of  the  adults, 
40,000  will  have  been  invalids,  5000  will  be  in  various  institutions 
for  mentally  or  physically  unfit,  and  100,000  will  be  inferior  to  the 
extent  of  reducing  their  value  as  citizens. 

School  examinations  in  Brooklyn  show  that  72  per  cent  of  the 
pupils  need  some  form  of  medical  treatment.  If  this  ratio  holds 
for  the  United  States  it  would  mean  14,000,000  children  who  are 
in  need  of  health  improvement.  These  figures  are  not  given  to 
cause  any  feeling  of  pessimism  or  discouragement,  but  rather  to 
show  what  great  need  there  is  for  civic  control  in  all  matters  per- 
taining to  health,  and  for  the  intelligent  cooperation  of  every 
citizen  in  these  measures. 

Already  modern  methods  of  hygiene  and  sanitation  have  added 
fifteen  years  to  the  human  life.  In  the  Spanish  war  we  lost  four- 
teen men  by  disease  for  every  one  that  died  of  wounds.  In  the 
Russo-Japanese  war,  with  modern  sanitary  precautions  in  force, 
the  Japanese  lost  only  one  by  disease  for  every  four  killed,  a  record 
fifty-six  times  as  good  as  ours. 

440 


CIVIC  BIOLOGY  441 

No  complete  figures  are  available  for  the  World  War,  but  it  is 
certain  that  never  before  have  the  modern  principles  of  sanita- 
tion, vaccination,  serum  treatment,  surgery,  and  the  relation  of 
insects  to  disease,  been  so  thoroughly  applied. 

Vaccination  against  typhoid  was  compulsory,  the  anti-tetanus 
serum  was  universally  used,  new  methods  of  treatment  for  in- 
fected wounds,  devised  by  Dr.  Carrell  and  others,  were  in  constant 
use.  Every  soldier  was  provided  with  iodine  to  sterilize  a  wound 
and  aseptic  bandages  to  make  a  temporary  dressing. 

As  a  result  of  these  various  applications  of  biologic  science  to 
army  methods,  the  loss  from  infectious  disease  was  very  low.  "  If 
the  Civil  War  death  rate  had  obtained  in  the  recent  war,  we  would 
have  lost  138,518  American  soldiers  from  typhoid,  dysentery, 
malaria,  and  small-pox  instead  of  273,  which  was  the  actual  num- 
ber," says  Dr.  Henry  Smith  Williams  in  one  report  (Dec.  1919). 

We  are  waging  a  winning  fight  against  disease  and  this  chapter 
will  touch  briefly  upon  some  of  the  methods  by  which  it  is  being 
carried  on.  We  are  all  soldiers  in  the  army  of  Public  Health  and 
cannot  be  too  well  informed  as  to  what  must  be  done  to  gain  com- 
plete victory. 

Food  Control.  Almost  every  town  and  city  has  regulations  as 
regards  food  inspection.  The  stores,  bakeries,  slaughter  houses 
and  milk  stations  are  under  supervision  of  official  inspectors. 
Foods  must  be  protected  from  flies,  bread  must  be  wrapped, 
food  animals  examined  as  to  their  health,  and  fair  weight  and 
measure  must  be  given  the  purchaser. 

Water  supplies  are  provided  at  enormous  expense,  the  water 
shed  is  carefully  guarded  from  pollution,  the  water  itself  is  filtered 
and  chemically  treated  to  remove  bacteria.  Chemists  and 
bacteriologists  are  constantly  employed  to  attend  to  these 
matters. 

Milk  has  always  been  a  prolific  source  of  disease  among  young 
children  and  every  means  is  now  taken  to  secure  its  purity  and 
freshness.  The  farmer  must  have  healthy  cows  and  healthy  men 
to  care  for  them,  he  must  have  clean  stables  and  sterilized  cans 
and  utensils.  The  inspectors  of  state  or  city  enforce  a  list  of  rules 


442  BIOLOGY  FOR  BEGINNERS 

covering  in  some  cases  over  sixty  items  that  tend  toward  supply- 
ing clean  milk  to  the  dealer  in  the  city. 

The  dealer  is  again  subject  to  equally  careful  control.  He  must 
not  let  the  milk  get  warmer  than  fifty  degrees,  he  must  provide 
clean  cans  and  handling  conditions,  he  must  sell  in  sealed  and 
labeled  bottles,  and  his  milk  must  be  subject  to  examination  for 
bacteria,  at  any  time.  If  any  of  these  conditions  are  found  danger- 
ous, the  milk  is  destroyed. 

Milk  normally  contains  bacteria,  mostly  harmless  and  some 
useful,  but  the  total  must  not  exceed  100,000  per  cubic  centimeter 
which  is  not  very  numerous  for  bacteria,  though  well-handled 
milk  ought  to  be  kept  far  below  this  limit.  Milk  must  have  at 
least  3.25  per  cent  of  butter  fat  and  must  not  contain  any  pre- 
servatives, such  as  borax,  soda,  or  formaldehyde. 

Sanitation.  Regulations  as  to  sewage  and  garbage  disposal  are 
in  force  in  most  cities,  and  means  are  provided  at  public  expense 
for  the  sanitary  disposal  of  all  wastes.  Stables  and  outhouses  are 
either  forbidden  or  restricted.  Factories  are  not  permitted  to 
pollute  the  air  or  water  with  their  waste  products. 

Streets  are  drained,  sprinkled,  oiled,  paved,  and  flushed  with 
water  to  remove  dirt  and  to  prevent  dust.  Trees  and  parks  are 
provided  to  improve  the  air  and  give  places  for  outdoor  rest  to  the 
population. 

Disease  Prevention.  It  is  in  this  department  that  modern  hy- 
giene has  made  its  greatest  progress.  We  now  provide  free  hos- 
pitals, clinics,  and  dispensaries  where  the  sick  may  receive  treat- 
ment. We  have  visiting  nurses,  city  physicians,  and  school  health 
'examinations  to  make  sure  that  all  who  need  help,  shall  receive  it. 
Stringent  laws  regulate  vaccination,  quarantine,  and  disinfection 
of  infected  premises.  Coughing,  sneezing,  and  spitting  are  for- 
bidden where  they  endanger  the  public  health,  and  the  public 
towel  and  drinking  cup  are,  fortunately,  things  of  the  past. 

Campaigns  of  education  by  printed  matter,  pictures,  school  in- 
struction and  lectures,  have  been  undertaken  by  city,  state,  and 
national  governments,  as  well  as  by  life  insurance  companies  and 
institutions  like  the  Rockefeller  Foundation. 


CIVIC  BIOLOGY  443 

As  a  result,  we  are  becoming  a  longer  lived  and  healthier  nation. 
Dirt,  vermin,  and  disease  are  recognized  as  alien  enemies  and  are 
being  removed  or  controlled. 

Factory  and  Housing  Conditions.  The  strongest  constitution 
cannot  endure  dark,  ill- ventilated  or  crowded  homes  and  factories. 
Laws,  inspection,  and  information  are  being  combined  to  bring 
about  better  conditions. 

In  most  states  child  labor  is  forbidden  or  restricted,  housing 
conditions  are  looked  after  to  some  extent  and  fire  protection  is 
usually  well  provided. 

To  carry  out  these  many  lines  of  civic  biology,  cities  and  towns 
usually  have  a  Board  of  Health,  inspectors,  and  the  assistance  of 
the  police.  In  large  cities  public  laboratories  are  maintained  where 
examinations  of  food,  milk,  water,  and  disease  cultures  are  made. 
There  may  be  one  or  more  city  physicians,  city  chemists,  and  visit- 
ing nurses  who  help  enforce  and  carry  out  the  regulations. 

The  street  cleaning  and  fire  departments  perform  their  obvious 
part  as  well  as  the  city  engineers  who  look  after  the  drains,  sewers, 
and  parks. 

The  Federal  government  devotes  much  of  the  work  of  the  De- 
partment of  Agriculture  and  the  Department  of  Commerce  and 
Labor,  to  matters  pertaining  to  national  health  and  the  conserva- 
tion of  natural  resources.  They  distribute  quantities  of  valuable 
literature,  and  carry  out  investigations  along  varied  lines  of  civic 
biology. 

The  Federal  "  Pure  Food  and  Drugs  "  law  was  enacted  in  1906 
and  regulates 

1.  Inspection  of  all  food  animals. 

2.  Standards  of  purity  for  food  products. 

3.  Freedom  from  adulteration. 

4.  Prevention  of  harmful  preservatives. 

5.  Proper  labeling  of  drugs  and  medicines. 

6.  Proper  labeling  of  package  goods. 

Patent  Medicines.  The  consumption  of  patent  medicines  costs 
the  people  of  the  United  States  $200,000,000  per  year.  This  would 


444  BIOLOGY  FOR  BEGINNERS 

be  well  enough  if  the  people  were  benefited  by  their  use,  but  this  is 
rarely  the  case.  On  the  other  hand,  most  of  them  are  fakes,  some 
are  positively  dangerous,  all  are  outrageously  expensive,  and  in 
many  cases  their  use  delays  proper  treatment,  till  too  late. 

The  Food  and  Drugs  law  obliged  them  to  make  no  claims  to 
"  cure  "  unless  they  could  prove  their  claims  and  this  rule  has 
practically  removed  that  word  from  their  vocabulary  of  fiction. 

No  patent  medicine  ever  cured  consumption,  nor  "  kidney 
trouble,"  nor  catarrh,  and  they  now  are  more  careful  in  the  wording 
of  their  advertisements,  though  they  still  try  to  convey  the  same 
impression. 

"  Consumption  cures  "  are  mainly  opiates  which  lull  the  suf- 
ferer into  false  security  until  past  all  help.  Tonics  and  sarsapa- 
rillas  depend  wholly  upon  alcohol  for  their  effect.  "  Soothing 
Syrups  "  for  helpless  babies  are  opium  and  morphine  mixtures 
and  frequently  lay  the  foundation  for  drug  habits  in  later  life,  if 
indeed  the  baby  is  not  "  soothed  "  into  the  sleep  that  knows  no 
waking. 

Headache  remedies  are  all  heart-depressing  drugs  which  deaden 
the  pain  but  do  not  remove  the  cause,  of  which  the  pain  was  merely 
a  warning. 

Catarrh  cures  are  usually  cocaine  or  opium  mixtures  and  often 
lead  to  drug  addiction;  under  recent  laws  they  are  much  restricted. 

The  Food  and  Drug  Law  does  not  forbid  the  sale  of  these  medi- 
cines but  it  does  oblige  the  maker  to  do  two  things : 

1.  He  must  put  on  the  label  the  amounts  of  alcohol,  morphine, 
cocaine,  opium,  or  other  harmful  drug  which  his  medicine  contains. 

2.  He  must  not  "  make  any  false  or  misleading  statement  " 
as  to  the  virtues  of  his  particular  "  remedy." 

This  is  one  of  the  chief  values  of  the  law  and  applies  to  food 
stuffs  as  well  as  medicines,  so  the  only  way  to  obtain  the  protection 
which  the  law  affords,  is  by  reading  the  labels  before  you  buy. 

One  can  often  judge  of  the  character  of  a  newspaper  or  maga- 
zine, from  the  number  and  kind  of  patent  medicine  advertisements 
which  it  carries.  A  reputable  periodical  will  not  now  open  its 
columns  to  the  false  and  misleading  claims  which  some  medicine 


CIVIC  BIOLOGY  445 

manufacturers  offer.    Look  over  the  literature  that  comes  to  your 
home  and  draw  your  own  conclusions. 

COLLATERAL   READING 

Principles  of  Health  Control,  Walters,  pp.  373-396;  Civics  and  Health, 
Allen,  entire;  The  Human  Mechanism,  Hough  and  Sedgwick,  pp.  477-540; 
A  Handbook  of  Health,  Hutchinson,  entire;  Community  Hygiene,  Hutchin- 
son,  entire;  Civic  Biology,  Hunter,  pp.  373-396;  Town  and  City,  Jewett, 
entire;  Sanitation  Practically  Applied,  Wood,  see  index;  Handbook  of 
Sanitation,  Price,  see  index;  Sanitation  in  Daily  Life,  Richards,  look 
through. 

Bulletins  of  U.  S.  Department  of  Agriculture,  State  Departments  of 
Health,  Rockefeller  Foundation,  City  Health  Departments. 


SUMMARY 

1.  Our  responsibility  for  welfare  of  others. 

2.  The  needs,  as  shown  by  health  conditions. 

3.  Results  of  modern  methods  of  hygiene. 

4.  Food  control. 

Food.     Water.     Milk. 

5.  Sanitation. 

Sewage  and  garbage  disposal. 

Building  restrictions. 

Care  of  streets,  parks,  and  trees. 

6.  Disease  prevention. 

Free  care  for  the  sick. 

School  examinations  and  clinics. 

Laws  as  to  spitting,  etc. 

Education  in  hygiene  and  cleanliness. 

National,  state,  and  individual  publications  and  help. 

7.  Factory  and  housing  conditions. 

Laws  as  to  conditions  and  hours  of  work. 

Laws  as  to  child  labor.     Compulsory  school  attendance. 

Various  boards  and  inspectors  to  carry  out  work  in  Civic  Biology. 

8.  The  Pure  Food  and  Drugs  Law. 

9.  Patent  medicines. 


CHAPTER  XLVI 
THE  ECONOMIC  BIOLOGY  OF  PLANTS 

Vocabulary 

Economic,  pertaining  to  man's  use. 
Solvent,  a  substance  used  to  dissolve  others. 
Utilize,  to  use. 

Economic  biology  deals  with  the  relation  of  living  things  to  man, 
either  for  use  or  for  harm.  The  "  economic  importance  "  of  a  plant 
or  animal  does  not  mean  merely  its  value  to  man,  but  also  includes 
any  way  in  which  it  may  damage  him.  Usually  the  uses  out- 
number the  injuries,  but  do  not  forget  that  both  are  included. 

General  Uses  of  Plants. 

1.  To  supply  oxygen  and  remove  carbon  dioxide  in  photo- 
synthesis. 

2.  To  aid  in  returning  nitrogen  compounds  to  the  soil. 

3.  To  regulate  drainage  of  water  (forests). 

4.  To  supply  foods  for  man  and  animals. 

5.  To  provide  fabric  fibers  (cotton,  linen,  hemp). 

6.  To  provide  fuel  (wood,  peat,  and  coal). 

7.  To  provide  paper  materials. 

8.  To  provide  timber,  cork,  rubber. 

9.  To  provide  tanning  materials  (hemlock,  oak  and  other  barks) . 

10.  To  provide  dye  stuffs. 

11.  To  provide  drugs  and  medicine,  alcohol. 

12.  To  provide  turpentine,  wood  alcohol,  acetic  acid. 

To  balance  this  long  list  of  uses  for  plant  products,  there  are 
but  few  ways  in  which  they  ever  harm  mankind.  Some  of  these 
have  been  studied  in  Chapter  17. 

Of  course  bacteria  head  the  list  of  harmful  plants,  in  that  they 
cause  many  diseases,  but  do  not  forget  that  most  bacteria  are 

446 


THE  ECONOMIC  BIOLOGY  OF  PLANTS  447 

useful  and  that  some  disease  germs  are  not  bacteria  at  all,  but  are 
protozoan  animals.  Other  fungi  also  cause  harm  to  man's  crops 
and  foods;  among  these  are  the  rusts,  molds,  smuts,  and  mildews, 
which  have  also  been  studied  before.  Some  plants  are  poisonous 
and  do  a  little  harm  in  that  way;  among  these  may  be  mentioned 
certain  mushrooms,  poison  ivy,  water  hemlock,  etc.  In  cultivated 
land,  many  wild  plants  cause  harm  by  interfering  with  crop  growth. 
We  call  these  "  weeds  "  and  they  demand  much  labor  and  expense 
for  their  control. 

We  shall  now  take  up  some  of  the  economic  applications  of  plant 
biology  in  detail.  - 

Oxygen  Supply.  The  importance  of  plants  as  a  source  of  oxygen 
and  in  removal  of  carbon  dioxide  has  been  explained  in  Chapter  13 
but  cannot  be  over-emphasized.  Without  this  action  of  plants,  the 
supply  of  oxygen  would  be  exhausted  and  no  animal  life  could  exist. 

Nitrogen  Fixation.  The  return  of  nitrogen  compounds  to  the 
soil  by  the  action  of  certain  bacteria  has  also  been  mentioned 
(Chapter  17)  and  is  one  of  the  ways  in  which  its  fertility  is  main- 
tained, while  the  natural  decay  of  the  plant  tissue  also  aids  in  this 
same  process. 

Control  of  Drainage.  The  regulation  of  drainage  is  brought 
about  by  the  forests,  which  act  like  enormous  sponges,  soaking  up 
the  rains  and  letting  the  water  filter  slowly  through  the  soil,  instead 
of  rushing  off  in  floods,  as  it  does  when  heavy  rains  fall  on  barren 
regions. 

Foods.  Cereal  Grains.  Of  all  plant  parts  used  for  food  by  man, 
seeds  are  the  most  important,  and  among  them  the  cereal  grains 
easily  take  first  place. 

These  cereals  (whence  the  name?)  are  the  fruits  of  various  grasses 
and  include  wheat,  corn,  rice,  rye,  barley,  oats,  etc.  They  con- 
stitute the  most  important  group  of  food  stuffs  used  by  man 
or  other  animals.  In  their  composition  these  grains  contain  but 
little  water,  hence  they  keep  well,  and  store  considerable  food  in 
a  small  bulk:  they  are  all  rich  in  starch.  Wheat  contains  much 
proteid  (gluten)'  and  corn  is  well  supplied  with  oil,  of  which  the 
other  grains  contain  but  little. 


448 


BIOLOGY   FOR  BEGINNERS 


The  proteid  of  wheat  makes  its  flour  produce  a  sticky  batter 
resulting  in  the  spongy  "  light  "  loaf  which,  no  other  grain  will 
yield.  Macaroni  is  another  wheat  product  that  depends  on  this 


FIG.  137  Wheat,  (Triticum  sativum,  Grass  Family, 
Graminea).  A  plant  and  flower-cluster  of  beardless  or 
"club"  wheat,  a  piece  of  the  zigzag  rachis,  a  spikelet,  a 
flower,  and  a  kernel.  (Baillon.)  From  Sargent. 

fact  for  its  wide  use.    The  lack  of  fat  in  most  cereals  is  made  up 
for  by  using  butter,  milk,  or  cheese  with  them  when  possible. 
All  cereals,  especially  if  the  whole  grain  be  used,  supply  phos- 


THE  ECONOMIC  BIOLOGY  OF  PLANTS  449 

phorus,  sulphur,  potassium,  calcium,  magnesium,  and  sodium 
compounds  which  are  so  essential  to  proper  rations.  (See  Chapter 
37.)  They  are  easily  cultivated,  ripen  quickly,  yield  largely,  and 
so  constitute  one  of  the  first  and  most  important  crops  raised  by 
man.  The  history  of  the  cereals  is  the  history  of  the  human  race, 
wheat  being  found  imbedded  in  Egyptian  brick  five  thousand  years 
old.  Other  grains  are  found  among  the  relics  of  the  Swiss  Lake 
dwellers,  perhaps  much  older,  while  the  Chinese  have  cultivated 
rice  for  over  four  thousand  years  and  corn  was  used  in  America 
long  before  the  dawn  of  history. 

Kinds  of  Cereals.  Wheat  is  the  most  important  vegetable  food 
in  Europe  and  America.  The  United  States  leads  in  its  production 
with  Russia  in  second  place.  Not  only  does  it  provide  the  white 
bread  of  the  world,  but  macaroni,  spaghetti,  vermicelli,  etc.,  are 
also  wheat  products. 

Rice  feeds  more  people  than  any  other  grain,  being  the  chief 
cereal  of  China,  India,  and  southern  United  States  and  it  is  esti- 
mated that  one-half  the  population  of  the  world  depends  upon  it. 

Corn  was  one  of  the  first  cereals  to  be  used  by  savage  tribes  be- 
cause it  is  easily  cultivated  in  almost  any  climate;  United  States 
also  leads  in  the  production  of  this  grain.  Not  only  is  it  valuable 
as  food  for  men  and  animals,  as  meal,  canned  or  fresh,  but  starch, 
corn  syrup,  glucose,  oil,  and  gluten  foods  are  among  its 
products. 

Oats  will  thrive  in  colder  climates  than  any  other  grain.  It  is 
the  principal  cereal  of  Scotland,  Norway,  Sweden,  and  Iceland, 
and  is  used  for  food  and  fodder  in  other  temperate  regions. 

Barley  also  endures  cold  but  will  thrive  in  warmer  regions  as 
well;  it  was  formerly  a  valuable  food,  but  is  now  more  used  for 
fodder  and  for  malt  to  make  beer. 

Rye  will  grow  in  poorer  and  rougher  soil  than  any  other  grain 
and  Russia  leads  the  world  in  its  production.  It  makes  the  com- 
mon "  black  bread  "  of  Austria,  Germany,  Russia,  and  Sweden. 

Buckwheat,  despite  its  name,  is  not  a  true  grain  and  while 
pleasant  in  flavor,  its  flour  has  little  food  value;  it  is  a  native  of 
northern  Asia  and  will  grow  in  poor  soil  in  temperate  climates. 


450 


BIOLOGY  FOR  BEGINNERS 


FIG.  138.  Rice  (Oryza  sativa,  Grass  Family, 
Gramineaf).  P,  upper  part  of  rice  plant,  one-quarter 
natural  size;  S,  a  spikelet  from  the  same;  w,  rain-guard 
or  ligule  at  base  of  leaf-blade,  inner  view;  natural  size. 
(Martius.)  From  Sargent. 


THE  ECONOMIC  BIOLOGY  OF  PLANTS 


451 


Legumes.     Next   in  importance   to   the    cereals    among    the 
seeds  used  for  food  are  the  legumes  (peas,  beans,  and  lentils)  all 


FIG.  139.    Peanut  (Arachis  hypoga,  Pulse  Family,  Leguminosai). 

A ,  lower  part  of  a  plant  showing  the  leaves  and  flowers  above  ground,  and 
ripening  nuts  and  roots  below;  the  surface  of  the  ground  indicated  at  el.  B,SL 
flower  cut  vertically  to  show,  at  the  base,  the  small  ovary  containing  the  ovules, 
and  the  long  style  extending  through  a  slender  tube  which  is  surmounted  by 
the  calyx  and  cirolla  and  is  continued  by  a  tube  formed  of  the  united  filaments. 
>C,  a  ripe  nut  cut  lengthwise  to  show  the  two  seeds.  (Tanbert.)  —  The  plant 
is  an  annual,  i.e.,  it  completes  its  life  from  seed  to  seed  in  one  year;  stems  and 
leaves  somewhat  hairy;  flowers  orange-yellow,  fruit  pale.  Soon  after  pollen 
has  come  upon  the  stigma,  the  stamens  and  corolla  are  shed  and  the  ovary  is 
carried  out  beyond  the  calyx  by  a  stalk  which  becomes  5-8  cm.  long,  and, 
bending  downwards,  soon  buries  the  little  ovary  in  the  ground.  Once  buried 
the  ovary  ripens  into  the  familiar  pod-like  nut.  If  it  fails  to  get  buried  the 
ovary  withers.  From  Sargent. 


452 


BIOLOGY   FOR  BEGINNERS 


members  of  the  pea  family  to  which  also  belong  the  clover,  lo- 
cust, etc. 

The  legumes  are  very  valuable  foods,  rich  in  proteid  and  starch, 
have  little  water  or  oil  and  hence  keep  well,  though  their  proteid 
(legumin)  is  not  so  easily  digested  as  animal  forms. 

Nuts.  Nuts  are  larger 
and  richer  in  proteid  and 
oil  than  grains  or  legumes 
but  are  less  used  for  food, 
because  the  crop  takes  too 
long  to  mature  and  is  too 
bulky  to  store.  Nuts  also 
contain  so  much  oil  that 
they  do  not  keep  nor  digest 
well. 

The  chestnut  has  little 
oil  and  more  starch  than 
other  varieties.  It  is  used 
for  food  in  Europe  as  are 
also  walnuts  and  pecans,  to 
some  extent,  while  the 
people  of  the  tropics  use 
coconuts,  peanuts,  and 
Brazil-nuts  because  cereals 
do  not  thrive  in  such 

climates. 

FIG.  140.  Coconut  Palm  (Cocos  r\*\*  Q  A  T?  A  r  f 
nucifera,  Palm  Family,  Palmacea}.  Plants 

in  fruit  showing  general  form.    (Baillon.)     fa  is  a  very  valuable  seed 
The  columnar  trunk  rises  to  a  height  of      food    product.       It    IS    the 
bears   bright  green   leaves      seed  Qf  ft  fleshy  beny  ^^ 

on  a  shrub  about  15  feet 
high.  Coffee  belongs  to  the  same  family  as  quinine  and  madder 
(a  dye  plant)  as  well  as  our  common  bluets,  partridge  berry,  and 
bed  straw,  and  grows  only  in  tropical  regions,  mainly  in  Brazil, 
Arabia,  and  the  East  Indies. 
Cocoa  is  more  valuable  as  a  food  than  coffee,  though  less  used. 


THE  ECONOMIC  BIOLOGY  OF  PLANTS 


453 


It  is  the  seed  of  a  small  tropical  tree  growing  in  South  and  Central 
America,  Africa,  and  Ceylon.  From  the  "  cocoa  bean,"  as  it  is 
called,  are  made  cocoa,  chocolate,  and  cocoa  butter.  It  must  be 


a 


FIG.  141.     Coconut. 

A ,  fruit,  showing  husk  cut  vertically  through  the  center,  revealing  the  hard 
shell  of  the  nut. 

B,  nut  viewed  from  below,  showing  the  lines  (a,  a,  a)  along  which  the  three 
pistils  are  united;  and  between  them  the  three  germ  pores,  from  the  lower  one 
of  which,  ordinarily,  the  single  germ  emerges  in  sprouting. 

C,  lengthwise  section  through  the  fruit  sprouting;    notice  the  thick  husk, 
into  and  through  which  the  young  roots  grow,  the  hard  shell  of  the  nut  (black) 
within  which  is  the  layer  of  solid  seed  food  (coarsely  dotted),  and  the  liquid 
food  or  "milk"  (white)  into  which  the  enlarging  cotyledon  or  seed  leaf  (finely 
dotted)  pushes  its  way  and  acts  as  an  organ  of  absorption.    (Warming.)    The 
husk  is  smooth  and  grayish  brown,  and  is  largely  composed  of  coarse,  tough 
fibers.     From  Sargent. 

observed  that  cocoa  has  nothing  whatever  to  do  with  the  coco- 
nut which  is  a  palm  fruit  while  still  another  plant  (coca)  furnishes 
from  its  leaves  the  dangerous  drug  cocaine. 


454  BIOLOGY  FOR  BEGINNERS 

Notice  the  different  spellings:  COCOA,  beverage,  chocolate; 
COCONUT,  food  product,  palm;  COCA,  plant,  cocaine. 

Another  valuable  group  of  seed  products  includes  many  spices, 
such  as  mustard,  nutmeg,  mace,  anise,  celery,  and  caraway,  while 
castor  oil  and  strychnine  are  important  medicines  obtained  from 
seeds. 

Many  seeds  produce  useful  oils  among  which  should  be  mentioned 
cotton-seed,  peanut,  and  almond,  which  are  used  for  food;  cocoa 
and  corn  oils  for  soap  and  linseed  (flax)  oil  for  paints. 

In  all  these  important  foods  that  man  obtains  from  seeds,  he  has 
been  using  the  store  of  nourishment  intended  for  use  by  the  em- 
bryo plant.  Most  seeds  "  keep  "  well  and  have  a  very  concen- 
trated store  of  food,  an  adaptation  for  reproduction  of  the  plant, 
which  man  has  utilized  for  his  own  benefit. 

Root  Food  Materials.  Roots  furnish  a  large  part  of  one  of  man's 
most  valuable  foods,  namely,  sugar.  Sugar  beets  now  produce 
over  half  the  world's  supply  of  "  granulated  "  or  "  white  "  sugar; 
the  rest  comes  from  the  stem  of  the  sugar  cane.  Other  products 
from  the  beet-sugar  industry  are  potash  for  glass-making,  fodder 
for  cattle,  and  waste  for  fertilizer. 

Among  our  common  garden  vegetables  we  have  the  roots  of  beet, 
turnip,  carrot,  radish,  parsnip,  and  sweet  potato  (not  the  common 
potato,  which  is  an  underground  stem). 

Ginger,  licorice,  rhubarb,  marshmallow,  tapioca,  and  aconite 
are  all  root  products,  used  for  food  or  medicines. 

Stem  Food  Materials.  Stems  provide  many  forms  of  food  among 
which  the  sugar  cane  takes  the  lead  and  the  potato  comes  next  in 
order. 

Potatoes  are  used  directly  as  food,  and  also  furnish  starch  and 
dextrine,  the  latter  being  the  gum  used  on  stamps,  labels,  etc., 
and  also  for  finishing  many  kinds  of  cloth. 

The  pith  of  a  certain  palm  stem  furnishes  sago  starch  and  pearl 
tapioca  while  arrow-root  starch  is  from  the  underground  stem  of 
a  West  Indian  plant  and  is  the  most  easily  digested  of  all  starches. 
Cinnamon  bark,  asparagus,  camphor,  and  witch  hazel  are  food  and 
drug  products  also  derived  from  stems. 


THE  ECONOMIC  BIOLOGY  OF  PLANTS  455 

Leaf  Food  Products.  We  usually  think  of  leaves  as  fodder  for 
animals  (grass,  hay,  etc.),  but  notice  the  list  of  those  that  we 
commonly  use  ourselves.  We  must  include  the  garden  vegetables, 
cabbage,  lettuce,  celery,  spinach,  pie  plant,  parsley,  onion,  cress; 
the  flavors  of.  mint  and  wintergreen;  tea  and  tobacco;  and  the 
drugs,  cocaine  and  belladonna.  Although  leaves  have  little  real 
nourishment  in  them  because  not  intended  as  storage  places  for 
food,  yet  they  are  necessary  to  man's  diet,  since  they  supply  many 
of  the  mineral  salts,  especially  iron  and  potassium  compounds, 
which  are  essential  .to  health. 

Flowers.  Flowers  we  seldom  eat,  but  cauliflower  is  one  excep- 
tion, and  cloves  and  capers  are  both  flower  products. 

Fruits.  Fruits  furnish  an  extended  list  of  foods  for  man.  We 
classify  them  as  follows:  pomes,  such  as  apples,  pears,  and  quinces; 
stone  fruits,  like  the  peach,  plum,  cherry,  apricot,  and  prunes; 
citrus  fruits,  orange,  lemon,  grape  fruit;  simple  berries,  currant, 
grape  (raisin),  blueberry,  tomato;  compound  berries,  such  as 
raspberry,  strawberry,  and  blackberry;  gourd  fruits,  pumpkin, 
squash,  cucumber,  melon,  and  citron;  miscellaneous,  banana,  date, 
olive,  peppers,  vanilla,  allspice. 

Hops  and  opium  are  also  fruit  products  and,  though  not  foods, 
may  be  mentioned  at  this  point.  Like  leaves,  fruits  are  not  often 
very  concentrated  foods,  but  supply  sugar,  acids,  and  mineral 
salts  which  are  very  necessary  to  a  proper  diet. 

Foods  from  the  Spore  Plants.  The  spore  plants  furnish  but  little 
toward  man's  food,  mushrooms  being  the  only  ones  commonly 
eaten,  and  of  these  many  are  dangerous  and  the  best  only  one-sixth 
as  rich  in  proteid  as  meat. 

Iceland  moss  is  a  curious  lichen  sometimes  used  in  jellies  and 
medicines.  Though  we  do  not  eat  them  to  any  extent  we  must 
not  forget  that  we  could  not  do  without  spore  plants,  such  as  yeast 
and  certain  bacteria  that  help  in  preparing  such  important  foods 
as  bread,  butter,  and  cheese. 

Fiber  Plants.  Cotton  is  the  most  valuable  plant  fiber;  it  is  an  out- 
growth of  the  outer  coat  of  the  cotton-seed,  intended  to  aid  in  its 
dispersal,  and  consists  of  strong,  twisted  fibers  very  well  adapted 


456 


BIOLOGY  FOR  BEGINNERS 


FIG.  142.  Sugar-cane  (Saccharum  officinarum,  Grass  Family,  Gramineai). 
Plant  in  flower.  A,  part  of  spike,  showing  long  silky  hairs.  B,  spikelet  de- 
tached. C,  flower,  showing  stamens,  pistil  and  lodicules  at  the  base.  (Bentley 
and  Trimen.)  —  Perennial,  attaining  a  height  of  13  ft.;  stem  variously  colored, 
2-5  em.  thick.  From  Sargent. 


THE  ECONOMIC  BIOLOGY  OF  PLANTS  457 

for  spinning.  Not  only  is  cotton  made  into  thread  and  cloth, 
but  into  batting,  surgical  dressings,  paper,  celluloid,  and  gun 
cotton. 

Flax  which  is  the  bast  fiber  of  the  bark  of  the  plant  of  that  name, 
ranks  next  to  cotton  in  value.  From  it  are  made  linen  thread, 
cloth,  and  lace;  canvas,  duck,  carpet  warp,  oil  cloth,  fine  paper, 


FIG.  143.  Iceland  Moss  (Cetraria  islandica,  Shield-lichen  Family,  Parmc- 
liacece).  Plant,  natural  size,  growing  nearly  erect  from  dry  earth.  (Luerssen.) 
—  Upper  surface  brownish  or  olive,  pale  below,  often  red-stained  at  the  base; 
"fruit"  forming  chestnut-colored  patches  on  the  uppermost  lobes.  Native 
home,  North  America  and  Eurasia.  From  Sargent. 

and  parchment.  It  is  harder  to  prepare  than  cotton  and  is  grown 
chiefly  in  North  Europe. 

Jute  is  the  bast  fiber  of  certain  plants  of  India;  it  is  not  so  fine 
nor  durable  as  linen  but  is  made  into  burlap,  sacking,  webbing, 
and  cordage. 

Hemp  is  the  bast  fiber  of  a  member  of  the  nettle  family  and  is 
cultivated  largely  in  Europe  for  its  fiber  uses,  while  in  Asia  an 
intoxicating  drug  is  prepared  from  the  same  plant.  Hemp  is  coarse, 
but  stronger  than  flax  and  is  used  for  sail  cloth,  cordage,  and  oakum. 

Manila  fiber  is  obtained  from  the  leaves  (veins)  of  a  banana- 


458  BIOLOGY  FOR  BEGINNERS 

like  plant  of  the  Philippines.    From  this  are  made  the  best  ropes, 
binder  twine,  bagging,  and  sail  cloth. 

Coconut  fiber  comes  from  the  outer  husk  of  the  coconut  and 
is  used  for  cordage  and  for  the  familiar  brown  door  mats. 


FIG.  144.  Sea  Island  Cotton  (Gossypium  barbadense, 
Mallow  Family,  Malvacece).  Flowering  top,  j.  (Schu- 
mann.) —  Similar  to  upland  cotton  but  with  seed  black. 
Native  home,  West  Indies.  From  Sargent. 

Other  uses  for  vegetable  fibers  are  in  the  manufacture  of  cheap 
brushes,  brooms,  matting,  packing,  and  upholstery. 

Fuels.  The  next  topic  in  our  list  of  plant  uses  is  fuel.  While 
this  is  of  enormous  importance,  it  needs  little  explanation,  as  all 
are  familiar  with  coal  and  wood  and  must  know  that  gas  is  made 
from  the  former.  Peat  is  an  important  fuel  in  some  parts  of  Europe 


THE  ECONOMIC  BIOLOGY  OF  PLANTS 


459 


and  consists  of  the  partly  decomposed  and  compressed  peat  moss, 
similar  to  that  in  which  florists  pack  their  plants.    From  coal  are 


FIG.  145.  Flax  (Linum  usitaiissimum,  Flax  Family, 
Linaceas).  Plant  in  flower.  Young  flower-cluster. 
Seed,  entire  and  cut  vertically.  (Baillon. )  Annual, 
about  60  cm.  tall;  leaves  smooth;  flowers  light  blue; 
fruit  dry.  Native  home,  Southeastern  Europe  and 
Asia  Minor.  From  Sargent. 

also  obtained  a  vast  number  of  dyes,  medicines,  explosives,  and 
other  products  which  will  be  studied  in  chemistry. 

Paper  Materials.    All  forms  of  paper  are  made  from  plant  mate- 
rial, chiefly  from  wood  fibers  of  spruce,  poplar,  and  similar  trees. 


460 


BIOLOGY   FOR   BEGINNERS 


Cotton  waste,  linen,  and  jute  are  important  paper  materials  while 
in  Japan  the  young  stems  of  the  paper  mulberry  are  used. 

Timber.  The  matter  of  timber  structure  and  of  forest  products 
in  general  will  be  taken  up  later.  The  uses  of  timber  are  so  numer- 
ous that  only  a  few  can  be  mentioned;  among  these  are: 


General  building 
Ships 
Vehicles 
Pavements 
Railroad  ties 


Furniture 

Boxes 

Bridges 

Poles 

Mine  timbers 


FIG.  146.    Harvesting  cork.     (Figuier.)     From  Sargent. 

Willow,  ash,  and  hickory  are  split  for  making  baskets,  chairs, 
and  hats;  rattan  and  wicker  work  are  from  similar  sources.  Pine 
and  spruce  furnish  excelsior  for  packing.  Cedar  supplies  our 
pencils,  and  mahogany  and  other  fine  woods  are  cut  into  veneers. 

Two  other  very  valuable  tree  products,  though  not  timbers, 
are  cork  and  rubber.  Cork  is  obtained  from  the  bark  of  the  cork 
oak  which  grows  largely  in  Southern  Europe  and  is  used  not  only 
for  stoppers,  but  to  make  linoleum,  life  preservers,  packing,  arti- 
ficial limbs,  handles,  etc. 


THE  ECONOMIC   BIOLOGY  OF  PLANTS  461 

Rubber  is  made  from  the  milky  juice  of  several  tropical  trees 
of  South  America  and  Asia;  its  uses  are  many  and  varied  and 
familiar  to  most  of  us. 

Tanning  Materials.  The  principal  tanning-  materials  are  ob- 
tained from  the  bark  of  the  oak,  hemlock,  willow,  birch  (Russia 
leather),  chestnut,  and  the  South  American  quebracho. 

Dye  stuffs.  Vegetable  dyes  have  become  much  less  important 
since  the  development  of  the  coal  tar  or  aniline  colors,  however 
indigo,  logwood,  and  gamboge  may  be  mentioned.  The  indigo 
plant  grows  in  India  and  Java  and  furnishes  the  familiar  blue 
dye;  logwood  grows  in  Central  and  South  America  and  fur- 
nishes red  and  black  dyes,  while  gamboge  is  a  yellow  dye  grown 
in  Siam. 

Drugs.  Several  drug  products  have  been  mentioned  elsewhere 
so  that  merely  a  brief  list  will  be  given  here : 

Gums:    Camphor  (China),  Arabic  (Africa),  Tragacanth  (Asia). 

Witch  hazel  from  leaves  and  stems  of  a  native  plant. 

Opium  from  milk  of  Chinese  and  Indian  poppy  fruits. 

Cocaine  from  coca  leaves  (Peru). 

Quinine  from  chinchona  bark  (Peru). 

Strychnine,  atropine,  and  nicotine  are  important  plant  drugs. 

Alcohol  is  one  of  the  most  important  plant  drug  products;  it 
has  a  multitude  of  uses  other  than  as  a  beverage.  It  is  utilized  in 
all  chemical  industries,  as  a  solvent,  fuel,  preservative,  and  in 
many  other  useful  ways. 

Alcohol  is  made  by  the  action  of  yeast  ferments  on  several  kinds 
of  sugars.  Apples,  rye,  and  corn  furnish  whiskey;  barley  malt 
is  used  for  beer;  grapes  provide  the  sugar  solution  for  wines; 
molasses  ferments  to  make  rum. 

All  of  these  and  some  waste  sugar  liquors  are  fermented  and 
distilled  to  make  commercial  alcohol. 

Distillation  Products.  The  last  topic  in  our  list  of  plant  uses 
includes  several  products  from  distillation  of  wood  or  pitch.  Crude 
turpentine  is  the  pitch  of  certain  kinds  of  pine  found  in  our  South- 
ern States,  France,  and  Russia.  From  it  the  common  turpentine 
is  made  by  distillation  and  rosin  is  left  as  a  residue.  Turpentine 


462 


BIOLOGY   FOR  BEGINNERS 


is  used  in  paints,  and  rosin  in  all  kinds  of  varnish,  soaps,  cements, 
and  soldering.     Wood  alcohol,  acetic  acid,  and  charcoal  are  all 


FIG.  147.  Dyer's  Indigo  Shrub  (Indigofera  tinctoria,  Pulse  Family,  Legu- 
minoscB).  Flowering  branch;  a,  flower,  enlarged;  b,  standard  (uppermost 
petal),  back  view;  c,  wing  (side  petal),  inner  view;  d,  e,  keel-petal,  inner  and 
outer  views;  /,  flower  with  corolla  removed;  g,  pistil;  h,  fruit,  natural  size; 
i,  seed;  k,  same,  cut  vertically.  (Berg  and  Schmidt.)  —  Shrub  growing  2  m. 
tall;  leaves  downy  beneath;  flowers  reddish  yellow;  fruit  dry.  Native  home, 
Southern  Asia.  From  Sargent. 


THE  ECONOMIC  BIOLOGY  OF  PLANTS  463 

made  by  distilling  any  kind  of  wood  in  large  closed  vessels.    It 
is  an  important  industry  in  many  wooded  regions. 

COLLATERAL   READING 

Elementary  Studies  in  Botany,  Coulter,  pp.  342-418;  Botany  for  Schools, 
Atkinson,  pp.  392-420;  The  World's  Commercial  Products,  Freeman  and 
Chandler,  entire;  Plants  and  their  Uses,  Sargent,  entire;  Elementary 
Biology,  Peabody  and  Hunt,  pp.  126-153;  Domesticated  Plants  and  Ani- 
mals, Davenport,  entire. 

SUMMARY 

Economic  biology,  the  relation  of  living  things  to  man,  whether  for  good 
or  harm. 

General  uses  of  plants. 

1.  Supply  oxygen,  remove  CO2.  7.  Paper  materials. 

2.  Regulate  drainage.  8.  Timber,  cork,  rubber. 

3.  Return  nitrogen  to  soil.  9.  Tanning  materials. 

4.  Foods  for  men  and  animals.  10.  Fabric  fibers. 

5.  Fuel.  11.  Dyestuffs. 

6.  Drugs,  medicines,  alcohol.  12.  Distillation  products. 

Harmful  plant  forms. 

1.  Some  bacteria  (disease). 

2.  Some  fungi  (destroy  crops,  timber,  etc.). 

3.  Poisonous  plants. 

4.  Weeds. 

Plant  uses  in  detail. 

1.  Oxygen  supply  (Chap.  13),  photosynthesis. 

2.  Nitrogen  fixation  (Chap.  17),  soil  bacteria,  decay. 

3.  Drainage  control  (Chap.  50),  forests  as  reservoirs. 

4.  Food  materials. 

Seed  products. 

Plant  Location  Uses 

1.   Cereals. 

Wheat  U.  S.,  Russia  Bread,  macaroni,  etc. 

Principal  food  of  white  races. 

Rice  China,  India  Feeds  half  the  world. 

Corn  North  America  Food,  fodder,  starch,  oil,  alcohol. 

Oats  North  Europe  Food,  fodder. 

Barley  Central  Europe  Fodder,  beer,  food. 

Rye  Europe  Dark  bread,  whiskev. 


464 


BIOLOGY  FOR  BEGINNERS 


2. 


3. 


4. 


Legumes. 

Beans 

Generally 

Peas 

cultivated 

Lentils. 

Nuts. 

Chestnut 

South  Europe 

Coconut 

Tropics 

Peanuts 

America 

Various  seeds. 
Coffee 
Cocoa 

Mustard        \  Various 
Nutmeg,  etc.  J 
Cotton-seed  1 
Peanut 

Almond'       Carious 
Flax,  cocoa  J 


important  as  proteid  foods. 


Food,  starch,  little  oil. 
Food,  fiber. 
Food,  oil,  butter. 


Asia,  S.  America  Beverage. 

S.  and  Cent.  Am.  Beverage,  chocolate,  butter. 

Spices  and  flavors. 

Oils  for  food,  soap,  paint. 


Root  products. 

Plant 


Sugar  beet 
"Vegetables" 
Beet,  carrot     Various 
turnip,  parsnip 


Location  Uses 

Europe,  U.  S.        Sugar,  potash,  fertilizer. 

Food,  supplying  starch  and  min- 
erals 


Sweet  potato 

Southern  U.  S. 

Food. 

Ginger 

India 

Spice. 

Licorice 

Mediterranean 

Flavor,  medicine. 

countries 

Rhubarb 

Various 

Medicine. 

Aconite 

Europe 

Medicine. 

Cassava 

Africa 

Food  starch. 

(tapioca) 

Stem  products. 

Plant 

Location 

Uses 

Sugar  cane 

U.  S.,  India, 

Food,  sugar,  molasses,  alcohol. 

West  Indies 

Potato 

U.  S.,  Europe 

Food,  starch,  dextrine. 

Sago  palm 

East  Indies 

Starch. 

Arrow  root 

West  Indies 

Starch. 

Asparagus 

Various 

Food. 

Cinnamon 

Ceylon 

Spice  from  bark. 

Camphor 

China 

Gum  for  medicine,  celluloid,  etc. 

THE    ECONOMIC    BIOLOGY    OF    PLANTS 


465 


Leaf  products. 


Fruits. 


Uses 
Food  (mineral  salts). 


Flavors. 

Beverage. 

Smoking  and  chewing. 

Drug  (cocaine). 


Pomes,  apple,  pear  Stone  fruits,  plum,  cherry,  peach. 

Citrous  fruits,  orange,  lemon         Berries,  grape,  currant,  tomato 
Comp.  berries,  strawberry,  etc.  Gourd  fruits,  squash,  pumpkin, 

cucumber. 
Various  fruits,  banana,  date,  olive,  vanilla,  hops,  poppy  (opium), 


Plant 

Onion,  cab- 
bage 
Lettuce,  rhu- 
barb 
Mint,  winter- 
green 
Tea 
Tobacco 
Coca 

Location 
Various 

Various 
India,  China 
Various 
S.  America 

Spore  plant  products. 

Mushrooms 
Iceland  moss  (jelly) 


5.   Fiber  plants. 

Plant 
Cotton 


Location 
India,  Egypt, 


Yeast  (in  making  bread). 
Bacteria    (in    making    butter, 
cheeses). 

Uses. 
Cloth,  paper,  explosives,  batting, 


Flax 
Jute 
Hemp 


United  States       dressings,  thread. 
North  Europe      Linen,  canvas,  paper,  lace. 


India 
Europe 


Manila  fiber    Philippines 
Coconut  fiber  Africa 


Burlap,  sacking,  cordage. 
Cordage,  sail  cloth,  oakum. 
Rope,  twine,  sail  cloth. 
Mats,  brushes,  upholstery. 

6.  Fuels. 

Wood,  charcoal,  peat,  coal,  gas  (by-products). 

7.  Paper. 

Spruce,  poplar,  etc.,  cotton  and  linen  waste. 

8.  Timber. 

Buildings,  furniture,  ties,  poles,  boxes,   baskets,   chairs,   pencils, 

excelsior,  veneers. 
Cork,  bark  of  cork  oak,  Southern  Europe. 

Stoppers,  life  preservers,  linoleum,  etc. 
Rubber,  juice  of  trees,  South  America  and  Asia 
Tires,  stoppers,  elastics,  raincoats,  etc. 

9.  Tanning  materials. 

Barks  of  oak,  hemlock,  willow,  birch,  chestnut,  quebracho. 


466  BIOLOGY  FOR  BEGINNERS 

10.  Dyestuffs. 

Indigo,  India,  Java  (blue). 

Logwood,  South  and  Central  America  (black  or  red). 

Gamboge,  Siam  (yellow). 

11.  Drugs. 

Gums,  camphor,  arabic,  tragacanth. 
Opium,  China,  India.     Milk  of  poppy  fruits. 
Cocaine,  Peru.     Leaves  of  coca  plant. 
Quinine,  Peru.     Bark  of  chinchona  plant. 
Alcohol  from  apples,  rye,  corn  —  whiskey. 
Alcohol  from  barley  malt  —  beer. 
Alcohol  from  grapes  and  fruits  —  wines. 
Alcohol  from  molasses  —  rum. 

12.  Distillation  products. 

Charcoal,  wood  alcohol,  acetic  acid,  turpentine,  rosin,  pitch,  tar. 


CHAPTER  XL VII 

THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES 

Vocabulary 

Polyp,  the  coral  animal,  which  is  not  an  "insect." 
Succulent,  juicy. 

Bivalves,  two-shelled  animals,  such  as  clams. 
Venomous,  poisonous. 

We  shall  take  up  the  economic  relations  of  animals  in  the  same 
way  as  we  have  plants,  giving  the  general  uses  and  harm  done 
and  then  taking  up  each  large  animal  group,  somewhat  in  detail. 

The  subject  is  so  broad  that  many  books  have  been  written  on 
the  economic  relations  of  insects,  birds,  or  mammals  alone,  so 
we  will  be  required  to  consult  reference  books  for  fuller  information. 

Try  especially  to  find  as  many  examples  of  each  case  as  possible, 
particularly  animals  which  are  familiar. 

General  Uses  of  Animals. 

1.  To  supply  food  (flesh,  eggs,  milk,  etc.). 

2.  For  transportation  (horse,  ox,  camel,  dog). 

3.  To  provide  fabric  fibers  (silk,  wool). 

4.  To  provide  fur  (seal,  mink,  otter). 

5.  To  provide  leather  (cattle,  sheep,  horse,  etc.). 

6.  To  provide  feathers. 

7.  To  provide  various  products,  such  as  ivory,  horn,  glue, 
gelatine,  hair,  etc. 

8.  To  aid  in  pollenation  and  seed  dispersal. 

9.  To  act  as  scavengers. 

10.  To  aid  in  destroying  harmful  animals  and  plants. 

Harmful  Kinds  of  Animals.  From  this  list  it  is  evident  that 
man  owes  about  as  much  to  other  animals  as  he  does  to  plants. 
There  are,  however,  a  few  harmful  exceptions. 

467 


468  BIOLOGY  FOR  BEGINNERS 

Certain  protozoa  cause  disease  (see  Chap.  18  and  25)  and  some 
parasitic  worms  (Chap.  20)  also  do  considerable  harm.  Many 
insects  live  upon  the  plants  that  man  also  uses  for  food  and  in  this 
way  cause  serious  destruction  to  crops,  while  others  transmit 
disease  (Chap.  25).  To  a  very  small  extent  "  wild  animals  "  harm 
man  directly  and  also  destroy  some  of  his  domestic  animals,  but 
this  is  of  comparatively  little  importance. 

Economic  Value  of  Animals.    In  dealing  with  the  economic  im- 


FIG.  148.    A  common  bath  sponge.    From  Kellogg  and  Doane. 

portance  of  animals  we  shall  take  them  up  by  groups  beginning 
with  the  simplest  first,  namely  the  protozoa. 

Protozoa.  These  minute  one-celled  forms  are  of  vast  importance 
to  man  insomuch  as  they  are  the  source  of  food  for  higher  animals 
and  these  in  turn  finally  provide  man  with  nourishment,  by  way 
of  such  important  sources  of  food  as  clams,  oysters,  crustaceans, 
and  fishes,  many  of  which  find,  in  protozoa,  their  chief  food  supply. 

Certain  protozoa  develop  minute  shells  and  the  deposits  of  these 


THE  ECONOMIC   BIOLOGY  OF  INVERTEBRATES     469 


tiny  skeletons  have  produced  great  layers  of  chalk  and  other  rock, 
which  form  important  land  areas  such  as  the  Dover  cliffs  in  southern 
England.  Some  of  the  pyramids  are  made  of  stone  formed  from 
protozoan  deposits. 

Many  protozoa  perform  valuable  service  as  scavengers,  and, 
since  they  are  mostly  aquatic,  aid  in  keeping  our  water  supply 
free  from  filth.  On  the  other  hand,  a  great  many  diseases  are  caused 
by  protozoa,  among  which  are  malaria,  smallpox,  yellow  fever, 
dysentery,  scarlet  fever, 
etc.  (See  Chap.  13.) 

Sponges.  From  the  next 
higher  group,  the  sponges, 
man  obtains  the  various 
forms  of  the  common 
"  sponge."  The  sponge  is 
really  the  horny  skeleton 
of  the  sponge  animal, 
from  which  the  jelly-like 
flesh  has  been  removed  by 
rotting  and  washing. 
Sponges  grow  attached  to 
the  sea  bottom  in  various 
warm  regions,  such  as  the 
Mediterranean  and  Red 
Seas,  and  Florida  and  West 
Indian  waters.  The  best 
come  from  the  Mediter- 
ranean. A  live  sponge  is  a  roundish  smooth  mass,  rather  dark 
brown  in  color,  provided  with  many  pores  for  passage  of  water, 
and  having  about  the  consistency  of  a  piece  of  beef  liver. 

They  are  collected  by  divers  or  by  dragging  hooks,  piled  on 
shore  till  the  flesh  rots  off,  washed,  dried,  sorted,  and  sometimes 
bleached.  The  world's  annual  sponge  crop  is  worth  about 
$4,000,000. 

Coelenterates.  The  coelenterates  include  many  curious  and 
beautiful  animals  such  as  the  hydras,  hydroids,  jelly-fish,  corals, 


FIG.  149.     Branching  coral  Acropora 


470 


BIOLOGY  FOR  BEGINNERS 


and  sea-anemones,  but  the  only  forms  directly  of  use  to  man  are 
the  corals.  Colonies  of  these  tiny  animals,  called  coral  polyps, 
secrete  so  much  limestone  in  their  body  walls  that  they  form  the 
coral  reefs  which  make  up  large  parts  of  several  continents,  notably 
Australia  and  the  Pacific  islands.  Other  coral  reefs  of  very  ancient 
times  now  form  important  beds  of  limestone  like  the  "  corniferous  " 
ledges  that  cross  central  New  York.  The  red  coral  used  for  jewelry 
is  another  product  of  this  group,  found  principally  in  the  Mediter- 
ranean. 

Echinoderms.  The  echinoderms  include  the  starfish,  sea-urchin, 
and  sea-cucumber.  Starfish  are  an  enemy  of  the  oyster  and  a 
special  effort  is  made  to  keep  them  out  of  oyster  beds.  The  Chinese 
and  West  Pacific  peoples  also  use  the  sea-cucumbers  for  food,  as 
soup,  and  consider  them  a  great  delicacy. 

Worms.  As  already  stated  in  our  study  of  worms  (Chapter  20), 
we  owe  to  the  humble  earthworm  a  heavy  debt  for  his  services  in 

keeping  the  soil  in  fertile 
condition;  and  we  must  not 
forget  that  without  this  work 
we  should  probably  have 
much  difficulty  with  our 
agriculture.  On  the  other 
hand,  the  parasitic  worms, 
such  as  tape-worm,  hook- 
worm, trichina,  and  other 
intestinal  forms,  cause  serious  disease  or  death  in  man.  Similar 
forms,  the  flukes,  infect  our  domestic  animals,  especially  sheep, 
which  they  attack  by  way  of  the  liver  and  cause  the  death  of 
hundreds  of  thousands  every  year. 

Molluscs.  Primitive  man,  before  he  knew  the  use  of  fire,  de- 
pended upon  raw  molluscs  for  much  of  his  food,  as  the  enormous 
shell  heaps  remaining  to  this  day  testify.  Even  yet  we  look  upon 
oysters,  clams,  mussels,  and  scallops  as  useful  foods  or  luxuries, 
depending  on  how  far  we  live  from  the  seacoasts  where  they  are 
caught.  In  all,  except  the  scallops,  we  eat  the  whole  body,  the 
bulk  of  which  consists  of  the  liver  and  reproductive  glands.  What 


FIG.  150.  Liver-fluke  (Fasciola  hepatica). 
(Nearly  twice  natural  size.)  From  Kellogg 
and  Doane. 


THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES     471 

we  hear  called  the  "  ears  "  are  really  the  muscles  that  held  the 
shell  together  and  it  is  this  muscle  only  which  we  eat  in  the  case 
of  the  scallop. 

Clams  are  found  along  our  whole  Atlantic  coast;  oysters  are 
abundant  south  of  Cape  Cod  with  Chesapeake  Bay  as  the  center 
of  the  industry,  having  the  largest  production  of  any  region  in  the 
world.  The  Pacific  coast  and  foreign  shores  also  furnish  these 
succulent  bivalves,  but  even  so,  Chesapeake  oysters  are  in  demand 
in  the  best  markets  of  Europe,  and  the  oyster  yields  the  most 
valuable  water  crop  in  existence.  It  is  the  leading  fishery  product 
in  fifteen  different  states.  Aside  from  their  value  as  food,  mol- 
lusc shells  furnish  us  with  "  mother-of-pearl  "  for  buttons,  handles, 
and  ornaments,  with  crushed  shell  for  chicken  feeding,  and  with 
the  precious  pearl  of  the  jewelry  store. 

These  latter  are  found  in  "  pearl  oysters  "  (not  the  edible  species) 
and  are  caused  by  the  entrance  within  the  shell  of  a  grain  of  sand  or 
the  irritation  of  a  parasitic  worm,  which  makes  the  oyster  secrete 
layer  after  layer  of  shell  substance,  to  cover  the  offending  particle, 
much  as  the  hand  protects  itself  from  irritation  by  growing  a 
callous  layer.  The  most  valuable  pearls  are  found  in  the  Persian 
Gulf  and  on  the  coasts  of  Ceylon.  Fresh-water  clams  furnish  the 
irregular  "  baroque  "  pearls  and  are  found  largely  in  the  Mis- 
sissippi and  its  branches. 

Shells  have  always  been  used  for  ornaments  and  formerly  passed 
for  money  as  well,  the  "  cowrie  "  of  Africa  and  the  "  wampum  " 
of  our  Indians  being  two  examples.  Wampum  consisted  of  beads 
cut  from  the  colored  parts  of  clam  shells. 

Snails  and  slugs  are  another  group  of  molluscs,  which,  especially 
in  France,  are  valued  as  food.  They  do  considerable  harm  in 
gardens  where  they  eat  young  seedlings  and  leaves.  The  shiny 
trails  so  often  seen  on  sidewalks  are  left  by  the  slugs  in  their  travels. 

A  near  relative  is  the  abalone  of  the  California  coast,  whose 
beautiful  rainbow  colored  shell  is  used  for  ornaments  and  for  a 
great  deal  of  inlaying  work. 

The  third  group  of  molluscs  is  called  the  cephalopods  and  in- 
cludes the  squid,  cuttle  fish,  and  octopus.  Man  uses  squid  for 


472 


BIOLOGY  FOR  BEGINNERS 


fish  bait,  and  obtains  from  the  cuttle  fish  the •  true  "  sepia,"  a  brown 
ink-like  pigment  which  the  animal  squirts  out  to  hide  itself  when 
attacked.  The  "  cuttle  bone  "  familiar  in  the  canary  cage  is  the 
internal  shell  of  this  same  mollusc. 

Crustacea.  The  larger  crustaceans,  lobsters,  crabs,  shrimps, 
and  prawns  are  valuable  sources  of  food  to  man;  the  smaller 
forms  are  equally  valuable  as  food  for  fish,  and  all  are  useful 
scavengers.  Of  all  these  the  lobster  is  most  valuable.  From  twenty 
to  thirty  million  are  annually  caught  along  the  coasts  of  New 
England  and  Canada  and  the  business  is  carefully  regulated  by 


FIG.  151.  The  giant  squid,  Ommatostrephes  calif ornica.  From  specimen 
with  body,  exclusive  of  tentacles,  four  feet  long,  thrown  by  waves  on 
the  shore  of  the  Bay  of  Monterey.  From  Kellogg. 

law  to  prevent  their  destruction  by  over  fishing.  "  Soft  shell " 
crabs  are  merely  the  ordinary  blue  crabs,  taken  just  after  moulting 
and  before  their  new  shells  have  formed. 

Barnacles  are  curious  crustaceans  which  attach  themselves  to 
rocks,  piles  and  even  to  the  bodies  of  whales  and  bottoms  of  ships. 
In  the  latter  place  they  interfere  with  easy  sailing  and  have  to  be 
removed. 

Acerata.  Spiders  as  a  whole  are  distinctly  beneficial  because 
of  their  destruction  of  flies  and  other  insects;  their  bite  is  seldom 
serious  to  man,  though  some  large  tropical  kinds  can  kill  small 
birds.  Scorpions  are  found  in  Southern  United  States  and  tropical 


THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES     473 


America  and  Africa;    their  abdomen  ends  in  a  venomous  sting, 
which,  while  painful,  is  seldom  fatal  to  man. 

"  Daddy-long-legs,"  which  belongs  to  this  group,  is  a  very  use- 
ful citizen  because  he  feeds  almost  entirely  on  plant  lice. 

Mites  and  ticks  are  degenerate  parasitic  forms  which  live  on 
the  blood  of  mammals  such  as  the  dog,  cattle,  and  man.  The 
itch  is  a  disease  produced  by  a  mite,  but, 
thanks  to  the  popularity  of  soap,  it  causes 
little  trouble. 

Insects.  The  economic  relations  of  in- 
sects are  so  important  and  complicated 
that  we  can  only  summarize  them  here. 
Refer  to  any  of  the  books  on  "  economic 
zoology  "  to  get  a  full  idea  of  their  im- 
portance. Over  half  of  all  insects  are 
harmful,  250  species  attack  the  apple, 
grape,  and  orange,  alone. 

As  to  their  harmful  activities,  they 

1.  Destroy  grain,  vegetables,  and  fruit 
crops. 

2.  Convey  many  kinds  of  disease  (flies 
and  mosquitoes). 

3.  Injure  domestic  animals   (flies  and 
mosquitoes,  etc.). 

4.  Destroy    buildings,     clothing,     etc. 
(white  ants  and  "  moths  "). 

5.  Annoy  and  injure  man  by  bites  and  stings. 

Their  total  damage  in  United  States  is  over  $200,000,000  per 
year. 

On  the  other  hand,  we  owe  to  the  insects  many  useful  processes 
and  products  such  as 

1.  Pollenation  of  flowers  of  valuable  plants. 

2.  Acting  as  scavengers  (maggots,  beetles). 

3.  Killing  injurious  insects  (lady  bugs  which  eat  scale  insects 
and  ichneumon  flies  that  destroy  tree  borers). 

4.  Furnish  silk  (silk  moth  cocoon). 


FIG.  152.  A  scorpion, 
Centrums  sp.,  from  Cali- 
fornia. (Natural  size.)  From 
Kellogg. 


474  BIOLOGY  FOR  BEGINNERS 

5.  Furnish  honey  and  wax  (bees). 

6.  Furnish  dye  (cochineal  red  from  a  scale  insect). 

7.  Furnish  shellac  (gum  secreted  by  a  scale  insect). 

8.  Furnish  ink  material  (gall  insects). 

The  following  are  some  of  the  common  injurious  insects,  which 
you  should  know  by  sight,  so  as  to  destroy  them  whenever  possible. 

FRUIT  TREE  PESTS 

Tent  Caterpillar.  Makes  web  nests  in  apple  and  cherry  trees. 
Caterpillar  dark,  with  white  stripe;  moths  light  brown  with  white 
stripe  on  front  wings;  eggs  in  belts  around  small  twigs.  Treat- 
ment: collect  and  burn  egg  masses;  destroy  nests;  spray  with 
poison  early  in  the  spring. 

Codlin  Moth.  The  familiar  "  apple  worm "  is  the  larva. 
Eggs  laid  in  young  apple  just  after  petals  form,  the  larva  hatches 
in  a  few  days  and  feeds  around  the  core,  making  the  "  wormy  " 
apple.  Treatment:  spray  with  poison  just  after  petals  have  fallen 
and  before  the  larva  can  get  inside  the  fruit  or  calyx.  This  in- 
sect costs  New  York  state  $3,000,000  per  year. 

Scale  Insects.  Small  circular  or  oval  scales  on  bark;  these  are 
the  bodies  of  the  females  under  which  eggs  are  deposited.  Each 
scale  insect  sucks  its  nourishment  from  the  juices  of  the  plant  and 
by  their  large  numbers  do  great  damage.  Treatment:  spray  with 
crude  petroleum  emulsion  before  buds  start  in  spring;  spray  with 
kerosene  or  whale  oil  emulsion  during  summer. 

SHADE  TREE  PESTS 

Tussock  Moth.  Handsome  caterpillars  with  three  black  tufts, 
four  white  tufts,  and  red  head.  Eggs  covered  by  frothy  white 
substance.  Treatment:  destroy  egg  masses  and  use  poison  sprays. 

Cottony  Maple  Scale.  Masses  of  cotton-like  scales  on  twigs 
and  leaves  suck  nourishment  from  tree  like  all  scale  insects. 
Treatment:  spray  with  kerosene  or  whale  oil  soap  emulsions. 

Borers.  Larvae  of  various  beetles  bore  under  the  bark  and  into 
wood,  loosening  the  bark,  and  killing  trees;  the  irregular  grooves 


THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES-    475 

under  old  bark  are  caused  by  them.    Treatment:  destroy  infested 
trees  or  branches;  dig  out  borers  in  fall;  encourage  the  birds. 

GARDEN  PESTS 

Potato  "  Bug."  A  beetle  whose  familiar  red  larva  .does  damage. 
Treatment:  spray  with  poison.  Arsenate  of  lead  is  better  than 
the  familiar  Paris  green. 

Squash  Bug.  A  true  bug;  bad  odor;  eggs  under  leaves;  feeds 
by  sucking  juices.  Treatment:  kill  adult  bugs  early  in  season 
to  prevent  egg  laying;  destroy  eggs. 

Cabbage  Worm.  Larva  of  white  or  yellow  butterflies.  Treat- 
ment: spray  young  plants  with  poison  or  dust  older  plants  with 
lime;  catch  adults  in  nets. 

HOUSEHOLD  PESTS 

Flies  and  Mosquitoes.    (See  Chapter  25.) 

Buffalo  Carpet  Beetle.  Adults  one-eighth  inch  long;  have  white 
and  red  markings,  may  be  brought  in  on  flowers;  larva  covered 
with  bristles;  eat  carpets,  feathers,  etc.  Treatment:  take  up 
carpets  and  spray  with  benzine  (outdoors);  fill  floor  cracks;  use 
rugs. 

Cockroaches  and  Croton  Bugs.  True  bugs;  scavengers;  very 
prolific.  Treatment:  use  poisons,  traps,  cleanliness. 

Clothes'  Moths.  Larva  of  small  gray  moth;  often  in  webbed 
cases;  attack  fur,  woolen,  etc.  Treatment:  frequent  brushing; 
tight  packing;  use  of  camphor  or  naphthalene;  cold  storage. 

It  will  be  noticed  that  some  insects  suck  their  food  by  piercing 
the  bark,  while  others  eat  the  foliage.  The  former  have  to  be 
treated  with  "  contact  poisons,"  like  oil  emulsions  and  whale  oil 
soap,  which  will  kill  if  they  touch  the  body.  The  latter  are  de- 
stroyed by  "  digestive  poisons,"  such  as  Paris  green  and  Hellebore, 
which  the  insects  eat  with  their  food. 

Among  the  beneficial  insects  we  should  learn  to  recognize  the 
"  lady  bug  "  a  red  beetle  whose  larvae  feed  on  plant  lice,  and  the 
lace  wing  fly  whose  larvae  also  favor  the  same  diet  and  thus  protect 
our  plants.  Another  useful  insect  is  the  long-tailed  Thallessa 


476  BIOLOGY  FOR  BEGINNERS 

with  ovipositors  two  to  four  inches  in  length.    This  insect  is  often 
feared  and  destroyed  when  really  it  lives  on  wood  borers  and  is 

very  useful. 

HARMFUL  LEPIDOPTERA 
Moths. 

Bee  moth,  eggs  laid  in  hive  at  night. 

Meal  moth,  webs  in  meal,  flour,  and  cereals. 

Leaf  rollers. 

Codlin  moth,  eggs  in  apple  blossoms;  larvae  are  " apple- worms." 

Currant  and  cherry  worms,  leaf  and  web  nests. 

Leaf  miners,  minute  larvae  eat  parenchyma  of  leaves. 

Clothes'  moths,  case  makers  in  woolens  and  furs. 

Peach  tree  borers,  attack  base  of  trees,  dangerous. 

Canker  worms,  "measure  worms." 

Currant  worm,  "measure  worms." 

Army  worm,  attacks  grains,  dangerous. 

Tussock  moth,  eats  shade  and  fruit  tree  leaves,  dangerous. 

Gypsy  moth,  leaf  eater,  dangerous. 

Tent  caterpillar,  maker  of  "worms'  nests,"  dangerous. 

Butterflies. 

Larvae  generally  harmful  in  some  degree  as  leaf  eaters. 
Cabbage  "worm,"  common  and  very  harmful. 

BENEFICIAL  BEETLES 

Tiger  beetles,  predaceous,  as  adult  and  larva,  on  insects. 

Ground  beetles,  predaceous,  very  numerous,  eat  caterpillars  and  potato 

beetles. 

Water  beetles,  eat  other  larvae,  snails,  small  fish,  and  decaying  vegetation. 
Carrion  beetles,  eat  dead  animals,  manure,  etc.     Bury  food. 
Rove  beetles,  eat  decaying  matter. 
Lady  bug  beetles,  eat  insect  eggs,  adults,  lice,  cottony  scale. 

HARMFUL  BEETLES 

Dermestids,  eat  fur,  wool,  carpet,  dried  meats,  museum  specimens. 
Click  beetles,  larvae,  wire  worms,  feed  on  grain  roots. 
Wood  borers,  larvae  in  trees. 
Stag  beetles,  live  on  wood  and  sap. 
Scarabs,  lamellicorn  beetles,  a  large  order, 

Scavengers,  dung  beetles. 

Leaf  eaters,  adult  on  leaves,  larvae  on  roots. 

Pollen  eaters. 

Buck  beetles,  wood  borers. 

Leaf  beetles,  potato  "bug,"  asparagus  and  cucumber  "bugs."     Grape. 
Weevils,  live  on  grains,  nuts,  fruits,  etc.,  very  harmful;    engraver  beetles 
under  bark. 


THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES     477 


INSECTICIDES 

Chewing  insects.     May  be  poisoned  in  food. 

Larvae  of  lepidoptera  and  coleoptera. 

Currant  worm  and  apple  worm. 

Potato  beetle  and  larvae. 

All  other  "worms,"  beetles,  and  "grubs." 
Sucking  insects.     Must  be  killed  by  contact  poisons. 

Plant  lice,  aphids. 

Scale  insects. 

True  bugs  (heteroptera). 
For  chewing  insects  use  digestive  poisons,  such  as 

Paris  green. 

Arsenats  of  lead. 

Hellebore. 
For  sucking  insects  use  contact  poisons,  such  as 

Whale  oil  soap         \forlice> 

Kerosene  emulsion  ; 

Lime-sulphur  wash  for  scale  insects. 
For  apples  use, 

2-3  Ib.  arsenate  of  lead,  1£  gal.  lime-sulphur,  50  gallons  water. 
For  peach,  plum,  cherry,  etc.,  use, 

2.  Ib.  arsenate  of  lead,  \  gal.  lime-sulphur,  50  gallons  of  water. 
For  winter  spraying  use  one  part  lime-sulphur  to  eight  water. 

FUNGICIDES 

Use  for  blight,  mould,  rust,  rot,  or  scab  the  following: 

Bordeaux  mixture. 

Dilute  lime-sulphur  wash,  as  follows: 
For  apples,  pears,  etc., 

\.\  lime  sulphur  to  50  gallons  water. 
For  plum,  cherry,  peach, 

\  gallon  lime-sulphur  to  50  gallons  of  water. 


COLLATERAL    READING 

Economic  Zoology,  Osborne,  pp.  1-300;  Insects  Injurious  to  Fruits, 
Saunders,  see  index;  Insect  Pests  of  Farm,  Garden  and  Orchard,  Sanderson, 
see  index;  Economic  Entomology,  Smith,  see  index;  Shell  Fish  Industry, 
Kellogg,  see  index;  Essentials  of  Biology,  Hunter,  Coral,  p.  210;  Worms, 
pp.  215-219;  Insects,  pp.  261-265;  Lobster,  228;  Molluscs,  pp.  269-271; 
Elementary  Biology,  Peabody  and  Hunt,  Bees  (A.  B.),  p.  42;  Insects  (A.  B.), 
pp.  13-22;  Crustacea  (A.  B.),  p.  162;  Protozoa  (A.  B.),  p.  173;  Applied 
Biology,  Bigelow,  Protozoa,  po.  312-316;  Worms,  pp.  340-345,  350; 
Crustacea,  p.  372;  Insects,  pp.  390-398;  Vegetable  Mould  and  Earthwormst 
Darwin,  Chap.  VII;  New  York  State  Museum  Bulletin,  No.  103  and  other 
N.  Y.  State  Bulletins;  Cornell  University  College  of  Agriculture,  Bui- 


478  BIOLOGY  FOR  BEGINNERS 

letins  Nos.  142,  234,  252,  283,  333  and  others.     Rural  School  Leaflets,  list 
on  application. 

U.  S.  Department  of  Agriculture  Bulletins,  Farmers'  Bulletins  Nos.  165 
264,  275,  564,  etc.,  Bulletin  No.  492,  etc.,  Circulars  Nos.  36,  98,  etc. 

The  above  Government  publications  are  merely  a  suggestion;  lists  can 
be  had  for  the  asking,  and  hundreds  of  useful  pamphlets  can  be  obtained, 
especially  in  regard  to  insects. 

(See  also  Chapter  25  on  "Insects  and  Disease.") 


SUMMARY 
General  uses  of  animals. 

1.  Food.  6.  Feathers. 

2.  Transportation.  .  7.  Ivory,  horn,  glue,  hair,  gelatine. 

3.  Fabric  fibers.  8.  Pollenation,  seed  dispersal. 

4.  Fur.  9.  Scavengers. 

5.  Leather.  10.  Destroying  harmful  forms. 

Harmful  kinds  of  animals. 

1.  Protozoa  (diseases). 

2.  Insects  (destroy  crops).     (Transmit  disease.) 

3.  Wild  animals  (destroy  man  and  domestic  animals). 

Economic  value  of  animals. 
Protozoa. 

1.  Food  for  higher  animals,  clams,  Crustacea,  fish,  etc. 

2.  Deposit  shell  as  chalk  beds. 

3.  Act  as  scavengers  in  water. 
Sponges. 

1.  Skeleton  of  horny  forms  used  as  "bath  sponge." 

2.  Preparation:   collected,  rotted,  washed,  dried,  bleached. 
Coelenterates. 

1.  Corals,  reef,  and  continent  builders. 

2.  Coral  deposits,  now  limestone  beds. 

3.  Precious  coral. 
Echinoderms. 

1.  Starfish  harmful  to  oysters. 

2.  Sea-cucumbers  eaten  by  Chinese,  etc. 
Worms. 

1.  Earthworms  necessary  in  cultivated  soil. 

2.  Parasitic  worms  cause  disease  in  man  and  animals. 
Molluscs. 

1.  Raw  food,  also  cooked,  clams,  oysters,  etc. 

2.  Shells  furnish  mother-of-pearl,  buttons,  chicken  feed. 

3.  Precious  pearls  (Persia  and  Ceylon). 

4.  Shells  for  money  and  ornament. 

5.  Squids  for  bait  and  cuttle  bone,  sepia. 


THE  ECONOMIC  BIOLOGY  OF  INVERTEBRATES     479 

Crustacea. 

1.  Lobster,  crab,  shrimp,  etc.,  for  food. 

2.  Small  forms  for  fish  food,  barnacles  harmful. 

Acerata. 

1.  Spiders  useful  in  killing  flies,  etc. 

2.  Scorpions  dangerous,  but  not  fatal. 

3.  Daddy-long-legs  feeds  on  plant  lice. 

4.  Mites  and  ticks,  parasitic  and  harmful  to  man  and  animals. 

Harmful  activities. 
Insects. 

1.  Destroy  crops.  3.   Injure  domestic  animals. 

2.  Transmit  disease.  4.    Destroy  clothing,  buildings. 

5.   Annoy  and  injure  man. 

Useful  activities. 

1.  Pollenation.  5.  Furnish  honey  and  wax. 

2.  Scavengers.  6.  Dyes. 

3.  Kill  injurious  insects.  7.  Shellac. 

4.  Silk.  8.  Ink  material. 

Common  Injurious  Insects. 
Fruit  tree  pests. 

Tent  caterpillar. 

Codlin  moth. 

Scale  insects. 
Shade  tree  pests. 

Tussock  moth. 

Cottony  maple  scale. 

Various  "borers." 
Garden  pests. 

Potato  "bug." 

Squash  bug. 

Cabbage  "worm." 
Household  pests. 

Flies  and  mosquitoes. 

Buffalo  carpet  beetle. 

Cockroaches,  croton  bugs. 

Clothes'  moths. 
Treatment. 

Sucking  insects  with  contact  poisons. 

Eating  insects  with  digestive  poisons. 
Useful  forms. 

Lady  bug. 

Thalessa  (an  ichneumon  fly). 

Carrion  beetles. 


CHAPTER  XL VIII 
THE  ECONOMIC  BIOLOGY   OF  VERTEBRATES 

Vocabulary 

Isinglass,  a  kind  of  gelatin,  not  the  substance  in  coal  stove  windows, 

which  is  mica. 

Appropriate,  to  take  away  for  use  (used  as  a  verb). 
Appropriate,  suitable  (used  as  an  adjective.) 

Fishes.  The  chief  value  of  fish  is  as  food,  both  for  other  animals 
and  for  man.  Out  of  12,000  known  species,  at  least  5000  are  valu- 
able as  human  food. 

The  annual  catch  of  salmon,  cod,  halibut,  mackerel,  and  herring, 
amounts  to  many  millions  of  dollars,  while  the  shad,  smelt,  perch, 
and  bass  are  almost  as  valuable.  The  Pacific  salmon  alone  are 
worth  about  $15,000,000  per  year  and  the  Atlantic  cod  returns 
about  $20,000,000.  In  fact  it  was  the  cod  returns  in  fisheries  that 
induced  the  settlement  of  New  England  and  pictures  of  this  cele- 
brated fish  may  yet  be  seen  in  the  state-house  of  Massachusetts, 
on  the  bank  notes  of  Nova  Scotia  and  the  postage  stamps  of 
Newfoundland.  The  fish  crop  of  Alaska  in  1915  amounted  to 
three  times  the  purchase  cost  of  the  whole  territory. 

Fish  are  eaten  fresh,  smoked,  salted,  dried,  pickled,  and  canned. 
Despite  these  various  ways  of  preparation  we  do  not  use  them  as 
extensively  as  we  should. 

The  Government  maintains  departments  of  fisheries  in  thirty- 
two  states  which  regulate  the  times  and  methods  of  catching, 
provides  hatcheries  for  artificial  raising  of  valuable  kinds  and  dis- 
tributes young  fish  to  stock  ponds  and  rivers,  so  that  the  supply 
may  not  become  exhausted. 

Another  important  use  for  fish  is  as  fertilizer  since  they  are 

480 


THE  ECONOMIC  BIOLOGY  OF  VERTEBRATES       481 

rich  in  phosphorous  compounds  which  most  plants  need.  The 
menhaden  is  much  used  for  this  purpose  as  well  as  for  its  oil.  In 
1913  over  a  billion  of  this  species  were  taken,  from  which  were  made 
6,500,000  gallons  of  oil  and  90,000  tons  of  fertilizer.  The  total 
weight  of  the  year's  catch  of  this  one  kind  was  more  than  the 
weight  of  all  the  inhabitants  of  Greater  New  York. 

Cod  liver  oil  is  the  easiest  oxidized  fat  food  in  the  world  and 
is  valuable  as  a  medicine.  Isinglass,  a  fine  quality  of  gelatine  is 
obtained  from  the  air  bladders  of  certain  fishes.  Glue  is  another 
important  product  made  from  waste  parts  and  bones  of  all  sorts 
of  fish. 

Amphibia.  The  chief  value  of  this  group  lies  in  its  activities 
in  destroying  harmful  insects.  Frogs,  toads,  and  salamanders, 
all  unite  in  feeding  upon  them,  the  toad  being  especially  useful 
in  this  respect.  To  a  very  much  less  extent,  frog  legs  are  used 
for  food;  frogs  might  much  better  be  left  to  fight  insects,  rather 
than  be  used  for  this  purpose. 

Reptiles.  We  usually  consider  this  group  as  useless  or  even 
harmful,  but  with  the  rare  exceptions  of  the  venomous  snakes, 
the  Gila  monster,  and  a  few  man-eating  crocodiles,  this  is  not 
true.  Most  snakes  destroy  either  insects  or  harmful  rodents, 
though  a  few  eat  frogs,  birds,  or  eggs. 

The  turtle  family  not  only  destroys  insects,  but  the  tortoise 
furnishes  flesh  and  eggs  as  foods  and  tortoise  shell  for  ornaments. 
Alligators  and  crocodiles  are  not  particularly  valuable  and  oc- 
casionally are  dangerous.  Their  hides  are  sometimes  made  into 
leather. 

Birds.  The  economic  value  of  birds  has  already  been  mentioned; 
they  are  our  chief  ally  in  the  fight  against  our  insect  enemies; 
they  provide  flesh  and  eggs  for  food;  they  supply  feathers  for 
bedding  and  ornament;  while  their  bright  colors  and  sweet  songs 
have  always  made  them  cheerful  companions  and  pets  for  man. 

In  order  to  preserve  these  valuable  members  of  society  we  can 

1.  Learn  to  observe  the  laws  made  for  their  protection. 

2.  Help  restrain  their  enemies,  the  plume  hunters,  game  hogs, 
cats,  red  squirrels,  black  snakes,  and  certain  birds  such  as  Cooper's 


482  BIOLOGY  FOR  BEGINNERS 

hawk,  sharp-shinned  hawk,  great  horned  owl,  and  English  spar- 
row. 

3.  Help  preserve  the  forests  and  city  trees  for  their  nesting. 

4.  Provide  winter  food  for  city  birds. 

5.  Provide  nesting  boxes  for  some  city  species. 

6.  Try  to  inform  others  along  these  lines. 

Mammals.  Food.  This  group  includes  the  animals  that  we 
usually  think  of  as  of  the  most  importance  to  man.  The  ungu- 
lates furnish  his  chief  sources  of  animal  food,  since  here  belong 
cattle,  sheep,  and  pigs,  and  many  others.  Man  uses  as  flesh  food 
practically  all  hoofed  animals  with  four  toes,  and  from  cattle  also 
obtains,  milk,  butter,  and  cheese.  Besides  these,  rabbits,  squirrels, 
bears,  raccoons,  opossums,  seals,  and  even  bats,  monkeys,  and 
whales  are  important  foods  for  man.  In  fact  all  mammals  ex- 
cept the  cat  and  dog. families  are  used  as  food  by  some  group  of 
people  or  other. 

Clothing.  Next  to  their  value  as  food,  the  mammal's  chief 
products  are  their  body  coverings,  which  man  appropriates. 
Sheep,  goats,  camels,  and  llama  all  produce  valuable  wools. 

The  list  of  fur-bearing  animals  includes  the  otter,  mink,  ermine, 
marten,  and  their  relatives,  together  with  foxes,  wolves,  bears, 
tiger,  leopard,  and  even  the  humble  skunk,  while  the  sea  otter 
and  seal  are  much  more  valuable.  The  seal  herd,  belonging  to 
the  United  States  is  the  most  valuable  Government  possession  in 
the  world.  Leather  is  obtained  from  the  hides  of  cattle,  sheep, 
horse,  hog,  goat,  seal,  walrus,  buffalo,  and  many  other  mammals 
and  is  absolutely  indispensable  because  it  has  no  satisfactory 
artificial  substitute. 

Various  Products.  The  whale,  largest  of  mammals,  provides 
several  curious  products;  oil  and  a  fine  wax  (spermaceti)  are  ob- 
tained from  some  kinds.  The  oil  whale  also  produces  "  whale 
bone  "  which  is  made  from  a  fibrous  strainer  device  developed 
from  the  roof  of  the  mouth.  Ambergris  is  an  abnormal  secretion 
of  the  liver  of  sperm  whales  which  is  of  enormous  value  as  a 
perfume. 

Horn  and  bone  products  of  many  mammals  are  used  for  making 


THE  ECONOMIC  BIOLOGY  OF  VERTEBRATES       483 

ornaments,  buttons,  handles,  etc.  Ivory  comes  from  the  tusks 
(teeth)  of  the  elephant  and  walrus. 

Transportation.  Of  much  greater  importance  than  these  last 
items,  is  the  use  of  many  mammals  as  beasts  of  burden.  The 
horse  is  easily  first,  with  oxen,  camels,  dogs,  goats,  llamas,  rein- 
deer, water  buffaloes,  and  elephants  used  in  different  countries  to 
a  greater  or  less  extent. 

Pets.  Mammals  have  been  used  by  many  as  companions  and 
pets;  in  this  class  the  dog  is  first,  the  horse,  cat,  and  occasionally 
other  forms  being  admitted  to  this  select  society. 

Among  the  mammals,  also,  are  most  of  the  "  domestic  "  ani- 
mals which  man  has  learned  to  tame  and  breed  for  many  of  the 
uses  just  mentioned.  Here  again,  the  dog  comes  first,  as  it  was 
probably  derived  from  a  domesticated  wolf  which  primitive  man 
tamed  for  his  company,  protection,  and  aid  in  the  hunt.  Prob- 
ably cattle  or  sheep  were  next  controlled  by  man,  though  the 
horse  may  have  preceded  them  in  learning  to  carry  his  master 
in  battle  or  the  chase.  To  this  list  man  is  still  adding  useful 
species  either  by  breeding  from  present  forms,  or  by  taming  new 
ones  when  their  value  is  discovered. 

The  other  side  of  the  account  is  represented  by  a  few  harmful 
mammals,  dangerous  either  to  man  himself,  to  his  domestic  ani- 
mals, or  to  his  crops.  Among  these  are  the  large  carnivora,  such 
as  the  tiger,  lion,  wolf,  etc.,  which  attack  man  or  his  flocks.  In 
this  country  carnivora  destroy  about  $15,000,000  worth  of  stock 
per  year.  The  rodents,  especially  rats,  mice,  and  squirrels  do 
enormous  harm  by  destroying  grains  and  other  food  stuffs.  In 
the  case  of  the  rat  alone,  the  wastage  amounts  to  about 
$200,000,000  annually.  Furthermore,  rats  and  some  squirrels  are 
infested  with  fleas  which  transmit  the  plague  to  man,  and  thus 
are  even  more  seriously  harmful.  As  a  whole  it  will  be  seen  that 
the  mammals  are  not  only  extremely  useful,  but  absolutely  essen- 
tial to  man;  without  them  our  present  civilization  and  mode  of 
life  would  be  impossible. 


484  BIOLOGY  FOR  BEGINNERS 

COLLATERAL   READING 

.  The  following  books  have  many  references  in  various  places;  see  index. 
Familiar  Fish,  McCarthy;  American  Food  and  Game  Fishes,  Jordan  and 
Everman;  American  Animals,  Stone  and  Cram;  American  Natural 
History,  Hornaday;  Our  Vanishing  Wild  Life,  Hornaday;  N.  Y.  Forest, 
Fish  and  Game  Commission  Reports;  The  Frog  Book,  Ditmars;  The  Reptile 
Book,  Ditmars;  Economic  Zoology,  Osborn,  from  page  311  to  end;  Useful 
Birds,  Forbush;  Economic  Value  of  Birds  to  the  State,  Chapman,  N.  Y., 
F.  F.  and  G.  Com.;  Birds  of  Eastern  North  America,  Chapman,  pp.  6-7; 
Bird  Life,  Chapman,  Chap.  I,  and  note;  Birds  of  Eastern  North  America, 
Reed,  pp.  12-14;  National  Geographic  Magazine,  November,  1916,  and 
May,  1918;  Domesticated  Plants  and  Animals,  Davenport;  Birds  in  their 
Relation  to  Man,  Weed  and  Dearborn. 


SUMMARY 
I.   Fishes. 

1.  Food  for  man  (5000  species). 

2.  Food  for  aquatic  animals. 

3.  Fertilizer. 

4.  Oil. 

5.  Glue,  isinglass. 

n.   Amphibia. 

1.  Destroyers  of  insects. 

2.  Food  (frog  legs). 

III.  Reptiles. 

Harmful  activities. 

1.  Venomous  snakes  (rattler  and  copperhead). 

2.  Venomous  lizard  (Gila  monster). 

3.  Man-eating  crocodiles. 

4.  Destroy  birds'  eggs  and  young  (black  snake). 

5.  Destroy  frogs  (black  and  garter  snakes). 
Useful  activities. 

1.  Destroy  insects. 

2.  Destroy  harmful  rodents. 

3.  Furnish  food  (turtle  meat  and  eggs). 

4.  Furnish  shell  (tortoise)  and  leather  (alligator), 

IV.   Birds. 

1.  Destroy  insects. 

2.  Destroy  weed  seeds. 

3.  Food  (flesh  and  eggs). 

4.  Feathers. 

5.  Companions. 


THE  ECONOMIC  BIOLOGY  OF  VERTEBRATES       485 

How  protect  birds? 

1.  Obey  and  enforce  protective  laws. 

2.  Restrain  their  enemies. 

(a)  Plume  hunters  and  game  hogs. 
(6)  Cats,  red  squirrels,  snakes. 

(c)    Cooper's  hawk,  sharp-shinned  hawk,  horned  owl,  English 
sparrow. 

3.  Preserve  forests  and  trees. 

4.  Provide  winter  food  and  summer  homes. 
V.   Mammals. 

1.  Food,  meat  and  milk  (ungulates) 

meat  (various  forms  except  dog  and  cat  groups). 

2.  Clothing,  wool  (sheep,  goat,  camel,  llama). 

fur  (rodents  and  carnivora). 
leather  (ungulates,  etc.). 

3.  Various  products. 

From  whale:  oil,  wax,  "whalebone,"  ambergris. 

From  elephant:   ivory. 

From  various  mammals:    horn  and  bone. 

4.  Transportation. 

Horses,  oxen,  camels,  reindeer,  dogs,  goats,  llamas,  water  buffalo. 

5.  Pets. 

Dogs,  horse,  cat,  etc. 
"Domestic  animals." 

6.  Harmful  mammals. 

(1)  Large  carnivora  (lion,  tiger,  wolf). 

(2)  Rodents  (rats,  mice,  squirrels). 

waste  foodstuffs, 
transmit  disease. 


CHAPTER  XLIX 
BIOLOGY  AND  AGRICULTURE 

Vocabulary 

Pulverizing,  making  into  powder. 

Tillage,  plowing,  cultivating,  harrowing,  or  hoeing  the  soil. 

Retain,  to  hold. 

Diminishing,  making  smaller. 

Civilization  rests  upon  the  soil.  In  so  far  as  our  knowledge 
enables  us  to  use  the  soil  to  best  advantage,  only  so  far  can  we 
advance  in  population,  wealth,  and  national  growth.  At  present 
we  are  far  from  realizing  our  greatest  agricultural  efficiency,  as 
the  following  tabulations  show. 

China         supports  3500    people    per    square    mile. 

Japan               "  2000 

Belgium           "  300 

United  States  "  30       " 

As  to  crop  yields  we  compare  as  follows, 

Maximum  yield  per  acre  U.  S.  yield  per  acre 
Potatoes                       500  bushels  96  bushels 

Wheat  50       "  14       " 

Corn  100       "  28       " 

Oats  100       "  32       " 

Evidently  there  is  much  to  be  learned  before  we  shall  obtain 
the  best  results  from  our  national  resources. 

Soil  Formation.  Soil  is  formed  from  rock  by  the  action  of  heat 
and  cold,  water  and  ice,  bacteria  and  protozoa,  which  are  all 
engaged  in  pulverizing  its  particles  and  adding  to  it  organic  matter 
and  nitrogen  compounds.  Proper  tillage  admits  air  for  plant  use 

486 


BIOLOGY  AND  AGRICULTURE  487 

and  carbon  dioxide  to  act  chemically  on  the  soil;  it  loosens  the 
soil  grains  to  permit  easy  root  growth  and  exposes  new  stores  of 
plant  food  for  them  to  absorb.  Loosening  the  top  layers  by 
frequent  tillage  also  forms  a  protective  layer  which  retains  water. 

Soil  Composition.  Plants  can  obtain  oxygen,  hydrogen,  and 
carbon  from  air  and  water,  but  must  depend'  on  the  soil  for  all 
compounds  of  nitrogen,  phosphorus,  and  potassium  which  are 
just  as  essential  in  the  making  of  protoplasm. 

To  be  fertile,  a  soil  must  contain  compounds  of  these  elements 
in  soluble  form,  available  for  plant  use.  The  average  soil  contains 
a  supply  of  potassium  compounds  sufficient  for  2000  years,  phos- 
phorous compounds  to  last  for  130  years,  but  nitrogen  compounds 
only  sufficient  for  70  years'  use.  Yet  nitrogen  compounds  are 
more  essential  and  used  in  greater  quantity  than  either  of  the 
others. 

Evidently  the  supply  of  nitrogen  is  the  limiting  factor  in  de- 
termining how  long  a  soil  will  remain  productive;  hence  its  return 
to  the  soil  is  one  of  the  greatest  problems  in  agriculture. 

Maintaining  the  Soil.  Every  crop  removes  these  essential 
elements  from  the  soil  and  erosion  may  rob  it  of  as  much  more, 
so  man  has  learned  to  replace  the  removed  substances  by,  1.  fer- 
tilizers, 2.  nitrifying  bacteria,  3.  crop  rotation. 

1.  Fertilizers   obtain   potash   as   potassium   chloride   and   sul- 
phate, largely  from  German  deposits.     Phosphorous  compounds 
are  obtained  from  bone  ash  and  the  phosphate  rock  found  in 
California  and  Florida.    Nitrogen  is  supplied  to  the  soil  by 

(a)  Natural  manures. 

(b)  Nitrate  of  soda  from  Chile. 

(c)  Slaughter  house  wastes. 

(d)  Ammonia  compounds  from  coal  distillation. 

(e)  Action  of  nitrifying  bacteria. 

A  complete  fertilizer  should  supply  all  three  elements,  but  as 
the  soil  often  has  enough  of  one  or  two,  this  is  sometimes  un- 
necessary and  analysis  of  the  soil  is  the  only  sure  way  of  deter- 
mining its  needs. 

2.  Bacteria,  found  in  nodules  on  the  roots  of  clover,  peas,  al- 


488  BIOLOGY  FOR  BEGINNERS 

falfa,  and  lentils,  have  the  power  of  converting  the  free  nitrogen 
of  the  air  into  nitrogen  compounds,  available  for  plant  use,  so 
clover  crops  actually  benefit  the  land  so  far  as  nitrogen  is  con- 
cerned. 

Other  bacteria  help  in  decay  of  organic  matter  and  return  it 
to  the  soil  in  useful  forms;  all  dead  tissue  and  natural  manures 
are  acted  upon  in  this  way. 

3.  Rotation  of  crops  merely  applies  what  has  just  been  said. 
The  farmer  cannot  use  the  same  field  for  the  same  crop,  year  after 
year,  without  removing  the  special  soil  compounds  which  that 
crop  requires  and  thus  diminishing  his  return.  He  therefore 
varies  his  crop  so  that  clover  or  peas  shall  have  a  chance  to  replace 
nitrogen  compounds  which  wheat  or  corn  may  have  removed. 
He  also  alternates  between  crops  that  require  hoeing  and  those 
that  do  not,  so  that  the  soil  may  benefit  by  the  different  methods 
of  cultivation.  Often  the  clover  crop  is  plowed  under  so  that  the 
organic  matter  as  well  as  the  nitrogen  is  returned  to  the  soil. 

Plant  Breeding.  Not  only  does  biology  bear  upon  soil  condi- 
tions .but  also  upon  all  that  relates  to  seed  planting,  germination, 
and  growth.  Especially  is  this  true  in  the  matter  of  testing  and 
selection  of  seed  and  in  crossing  and  breeding  of  new  varieties. 
A  glance  at  any  seed  catalog  will  show  the  great  advances  that 
are  being  made  by  applying  biologic  methods  to  bettering  the 
varieties  of  plants. 

In  this  same  connection,  all  other  methods  of  plant  propaga1 
tion  are  concerned.  Cuttings  and  grafts,  pollenation,  trans- 
planting, and  pruning  all  involve  the  use  of  biological  information. 

In  1900  the  British  Millers  Association  decided  that  the  wheat 
that  was  then  raised  in  England  was  so  unsatisfactory  that  they 
engaged  Prof.  R.  H.  Biffen  of  Cambridge  University  to  try  to 
improve  the  quality. 

Professor  Biffen  obtained  seed  of  all  the  different  wheats,  which 
had  any  one  desirable  characteristic,  such  as  stout  straw,  full 
heads,  immunity  to  rust,  or  resistance  to  cold  weather.  These 
he  raised  separately,  and  cross-pollenated  by  hand,  combining 
their  desirable  features,  till  after  years  of  effort,  selection,  crossing, 


BIOLOGY  AND  AGRICULTURE  489 

and  rejection  of  the  unfit,  he  developed  the  present  English  wheat 
which  combines  nearly  all  the  characteristics  which  the  millers 
demanded. 

In  the  United  States,  Mr.  Burbank  stands  at  the  head  of  our 
plant  breeders.  By  cross-breeding  and  rigid  selection  he  has 
developed  many  valuable  new  species.  His  improved  potato  adds 
$17,500,000  to  the  annual  income  of  the  farmers  of  the  United 
States.  He  has  increased  the  yield  of  some  kinds  of  corn  twenty 
fold.  He  has  improved  known  fruits  in  their  quality,  hardiness, 
or  resistance  to  insects.  He  has  developed  several  new  fruits, 
either  from  wild  species  or  by  crossing.  Many  large  and  beauti- 
ful flowers  have  been  produced,  such  as  the  mammoth  poppy 
with  a  diameter  of  ten  inches,  and  the  delicate  shasta  daisy.  One 
of  his  most  notable  successes  has  been  the  spineless  cactus,  which 
is  now  available  as  cattle  fodder  in  regions  where  it  is  difficult  to 
provide  food  for  stock. 

Burbank's  work  is  merely  a  very  noted  example  of  the  ap- 
plication of  biologic  laws  to  plant  improvement,  such  as  is  being 
carried  on  by  all  seedsmen  and  all  intelligent  farmers  and  gar- 
deners. When  we  save  seed  from  our  best  or  earliest  plants,  keep 
them  separate  from  less  satisfactory  kinds,  and  plant  their  seed 
again,  we  are  following  in  the  footsteps  of  these  great  breeders, 
and  utilizing  the  same  laws  of  inheritance. 

By  similar  methods,  practically  every  plant  that  man  culti- 
vates has  been  improved  and  developed  into  forms  that  better 
serve  his  purposes. 

Plant  Protection.  Biology  comes  to  the  aid  of  the  farmer  in 
his  struggle  against  plant  disease.  Moulds,  rusts,  blights,  and 
bacterial  attacks  all  have  to  be  met  by  proper  treatment  of  seed 
with  formalin,  or  the  plant  itself  with  fungus-killing  sprays  like 
Bordeaux  mixture. 

Insect  enemies  and  the  means  of  checking  them  open  another 
chapter  of  farm  biology.  Here  also  belongs  the  study  of  useful 
birds  and  their  enormous  value  as  insect  destroyers. 

Animal  Husbandry.  Principles  of  biology  are  also  applied  to 
animal  raising,  their  care  and  feeding,  selection  and  domestica- 


FIG.  153.  Various  races  of  pigeons,  all  probably  descended  from  the 
European  rock  dove,  Columba  lima,  shown  in  lower  right  hand  corner. 
(After  Haeckel.)  From  Kellogg. 


BIOLOGY  AND  AGRICULTURE 


491 


tion.  Especially  is  this  true  in  the  case  of  animal  breeding  for 
improved  varieties.  Here  are  involved  selection,  inheritance, 
and  cross-breeding. 

By  following  well-known  biologic  methods  man  can  select  al- 
most any  group  of  desirable  characteristics  and  produce  a  breed 
possessing  them.  As  evidence  of  this,  note  the  numerous  and 
widely  different  types  of  horse,  cow,  or  dog  that  man  has  thus 
developed. 

In  early  years  England  had  three  general  types  of  sheep,  — 


FIG.  154.    Typical  American  Merino  ewe,  a  highly  specialized  breed  of 
sheep,  with  fine,  close-set  wool.    (After  Shaw.)    From  Kellogg. 

some  hornless,  some  with  fine  wool,  and  some  producing  good 
mutton.  By  long  and  careful  breeding  and  by  rejecting  all  un- 
satisfactory animals  for  propagation,  they  now  have  several  races 
that  combine  in  a  large  degree  all  these  useful  features. 

In  similar  ways  we  have  different  breeds  of  cows  for  different 
purposes,  the  Jersey  producing  as  much  butter  fat  as  ten  ordinary 
cows,  the  Holstein  for  large  milk  production,  and  the  Hereford 
for  beef. 


FIG.  155.  Heads  of  various  British  breeds  of  domestic  cattle,  showing  varia- 
tions in  shape  of  head  and  condition  of  horns:  1,  Highland  Scot;  2,  Irish  Kerry; 
3,  Aberdeen  Angus;  4,  Hereford;  5,  Jersey;  6,  Long-horned  Midland.  (After 
Romanes.)  From  Kellogg. 


BIOLOGY  AND  AGRICULTURE  493 

Horses  for  trotting,  running,  draught,  or  mere  appearance,  are 
bred  and  selected  and  their  pedigrees  so  carefully  recorded  that 
many  a  trotter  can  trace  his  ancestry  much  farther  back  than 
most  human  aristocrats.  The  advantage  lies  with  the  horse  in 
another  way,  since  his  ancestors  were  valued  because  they  could 
do  something  well,  and  not  merely  because  of  the  accident  of  birth. 

Bacteria  on  the  Farm.  Care  of  milk  on  the  farm  has  been  al- 
ready mentioned,  but  in  cream,  butter,  and  cheese  as  well,  the 
farmer  is  using  some  bacteria  and  opposing  others.  The  char- 
acteristic flavors  and  odors  of  butter  and  cheese  are  due  to  use- 
ful bacterial  action, 'while  the  spoiling  and  decay  of  these  products 
is  due  to  attack  of  others. 

Bacteria  are  working  also  in  the  preparation  of  ensilage  and 
the  "  curing  "  of  meats  and  tobacco.  In  fact  if  you  will  look  back 
over  your  work  you  may  be  surprised  at  the  extensive  role  of 
bacteria  as  farm  laborers. 

Here  are  some  of  their  activities,  good  and  bad: 

They  aid  in  decay  of  organic  matter  for  fertilizers. 

They  cause  decay  of  valuable  foodstuffs. 

They  help  return  nitrogen  to  the  soil. 

They  cause  many  plant  and  animal  diseases. 

They  aid  in  all  dairy  processes. 

They  spread  disease  by  way  of  milk  and  other  foods. 

They  help  in  producing  ensilage. 

They  aid  in  curing  meats,  flax,  and  tobacco. 

There  is  no  branch  of  industry  so  important,  and  none  so  closely 
associated  with  biology  as  the  industry  of  agriculture.  Most  of 
the  material  found  in  the  chapters  on  economic  biology  both  of 
plants  and  animals,  together  with  much  under  forestry  and  gen- 
eral conservation  methods,  bears  directly  on  this  fundamental 
occupation. 

COLLATERAL   READING 

Agriculture  for  Beginners,  Burkett,  Stevens  and  Hill;  The  Fertility  of 
the  Land,  Roberts;  Soil  Fertility  and  Permanent  Agriculture,  Hopkins; 
Principles  of  Agriculture,  Bailey;  Farmers  for  Forty  Centuries,  King;  Fer- 
tilizers, Voorhees;  Practical  Agriculture,  Wilkinson;  First  Book  of  Farm- 
ing, Goodrich;  Cyclopedia  of  American  Agriculture,  Yols.  II  and  III; 


494  BIOLOGY  FOR  BEGINNERS 

Milk  and  Us  Products,  Wing;  Types  and  Breeds  of  Farm  Animals,  Plumb; 
Commerce  and  Industry,  Smith,  pp.  20-85;  Principles  of  Breeding,  Daven- 
port; Domesticated  Animals,  Shaler;  First  Principles  of  Agriculture,  GoS 
and  Mayne;  Science  of  Plant  Life,  Transeau,  pp.  217-232. 

PLANT  BREEDING 

Elementary  Studies  in  Botany,  Coulter,  pp.  326-339;  New  Creations  in 
Plant  Life,  Harwood,  entire;  Origin  of  Cultivated  Plants,  De  Candolle, 
entire;  Experiments  in  Plants,  Osterhout,  pp.  409-453;  Botany  for  Schools, 
Atkinson,  pp.  455-478;  The  Living  Plant,  Ganong,  pp.  426-444;  Species 
and  Varieties  (Mutation),  De  Vries,  entire;  Domesticated  Animals  and 
Plants,  Davenport,  entire;  Elementary  Biology,  Peabody  and  Hunt, 
pp.  105-125,  241-300. 

DOMESTIC  ANIMALS 

Elementary  Zoology,  Davenport,  pp.  420-450;  Domesticated  Animals 
and  Plants,  Davenport,  entire;  Economic  Zoology,  Kellogg  and  Doane, 
pp.  321-334;  Pet  Book,  Comstock,  entire;  Farm  Bulletins. 

SUMMARY 

1.  Importance  of  agriculture. 

2.  Lack  of  efficient  development. 

3.  Soil  formation. 

4.  Soil  composition: 

Potassium  compounds. 
Phosphorous  compounds. 
Nitrogen  compounds. 
Organic  matter  or  humus. 

5.  Soil  maintenance. 

By  fertilizers. 

By  bacterial  action. 

By  crop  rotation  and  cultivation. 

6.  Plant  breeding. 

7.  Plant  protection. 

From  insect  enemies. 
From  fungus  attack. 

8.  Animal  husbandry. 

Care  and  feeding  of  stock. 
Breeding  new  forms. 

9.  Bacteria  on  the  farm. 


CHAPTER   L 

THE  ECONOMIC  IMPORTANCE  OF  FORESTS 
Vocabulary 

Erosion,  washing  away  of  soil. 

Retention,  holding. 

Girdling  a  tree,  cutting  off  a  ring  of  bark  and  cambium  to  kill  it 

while  standing. 
Re-forestation,  scientific  replacement  of  trees  when  cut. 

The  great  importance  of  forests  is  little  appreciated.  When 
we  are  told  that  they  occupy  35  per  cent  of  the  area  of  the  United 
States  and  that  lumbering  is  our  second  largest  industry,  still 
their  most  important  services  are  overlooked. 

VALUE  OF  FORESTS 

Control  of  Water  Supply.  The  most  important  service  rendered 
by  forests  is  in  regulating  water  supply.  The  forest  area  acts  like 
an  enormous  sponge  absorbing  the  heavy  rainfall,  in  its  layer  of 
humus.  This  secures  the  following  important  results. 

1.  Prevents  floods  and  causes  steady  flow. 

2.  Prevents  drouth  by  storing  water  in  the  wet  season. 

3.  Prevents  washing  of  soil  into  rivers. 

4.  Keeps  rivers  at  uniform  level  for  transport. 

The  effect  of  forests  in  this  regard  can  only  be  appreciated  when 
compared  with  an  area  which  has  no  forest  protection  and  is  sub- 
ject to  heavy  rainfall,  such  as  the  Bad  Lands  of  Dakota.  Here 
the  water  runs  off  at  once  in  floods,  while  between  rains,  the  land 
is  almost  a  desert,  due  to  drouth,  and  the  rivers  are  so  filled  with 
mud  and  so  changeable  in  levels  as  to  be  useless  for  commerce 
or  power. 

495 


496 


BIOLOGY   FOR   BEGINNERS 


THE  ECONOMIC  IMPORTANCE  OF   FORESTS 


497 


Benefit  to  Soil.  The  early  settlers  regarded  the  forests  as  the 
enemy  to  agriculture  and  so  they  were,  in  so  much  as  some  clear- 
ings had  to  be  made  to  make  room  for  the  farms,  but  in  a  larger 
sense,  the  forests  are  a  distinct  benefit  to  the  soil.  Erosion,  the 
washing  away  of  soil  by  rain,  is  one  of  the  worst  enemies  of  ag- 
riculture and  this  is  prevented  by  the  forest  areas,  whose  roots 
hold  back  the  earth  and  whose  leaves  protect  the  surface.  Fur- 


FOREST   PRODUCTS    IN  1907. 


CLASSES 

FIREWOOD. 

LUMBER  AND  SHINGLES 

POLES,  POSTS.  AND   RAILS. 

HEWED  CROSS-TIES 

COOPERAGE    STCT,K 

PULP-WOOD. 

ROUND   MINE  TIMBERS 

DISTILLATION  WOOD... 


FOREST  MATERIAL  REQUIRED 
BILLIONS  Or  CUBIC  FEET 


Fig.  157.     Uses  of  Lumber.     From  Smith's  Commerce  and  Industry. 

thermore,  the  organic  matter  (humus)  which  collects  on  the  forest 
floor,  supplies  an  essential  element  to  all  fertile  soils. 

In  some  areas,  the  forests  perform  another  function  in  pre- 
venting the  spread  of  wind-blown  sand  over  fertile  areas  which 
are  thus  saved  for  use. 

Effect  of  Forests  on  Climate.  While  this  may  not  rank  with 
the  two  preceding  in  importance,  yet  it  is  certain,  that  by  its 
retention  of  moisture,  forests  do  modify  the  climate  over  large 
areas  and  apparently  influence  local  rain-fall  as  well.  To  a  less 


498  BIOLOGY  FOR  BEGINNERS 

extent,  forests  affect  climate  by  their  action  as  a  protection  from 
wind  or  sun. 

Forests  as  Home  for  Birds  and  Game.  This  is  a  matter  often 
overlooked,  but  when  we  recall  the  enormous  economic  value  of 
birds,  and  realize  that  they  depend  largely  on  the  forests  for  their 
home,  the  importance  of  this  factor  is  apparent.  As  a  home  for 
fur-bearing  animals,  game,  and  fish  the  forests  also  are  important 
to  man  in  many  relations  little  realized. 

Forest  Products.  When  the  economic  value  of  forests  is  men- 
tioned one  naturally  thinks  of  the  lumber  and  other  direct  prod- 
ucts as  the  most  important.  While  not  equal  to  those  already 
mentioned,  the  variety  and  value  of  the  manufactured  forest 
products  is  enormous. 

Time  will  not  permit  discussing  each  in  detail  so,  in  the  tabula- 
tion which  follows,  some  of  the  most  important  items  are  mentioned. 

FOREST  PRODUCTS 

1.  Timber  products. 

Lumber  Laths 

Shingles  Veneers 

Railroad  ties  Poles 

Mine  timbers  Ship  timbers 

2.  Paper  (spruce,  poplar,  etc.). 

3.  Fuel  (wood,  charcoal,  coal). 

4.  Naval  stores  (pitch,  tar,  turpentine,  rosin). 

5.  Tanning  material  (hemlock  and  oak  bark). 

6.  Maple  sugar. 

7.  Spruce  gum. 

8.  Distillation  products  Uses 

charcoal  fuel 

lamp  black  ink 

tar  tar  paper,  wagon  grease,  and  wood 

preservation 

oil  varnish,  soap,  disinfectants,  ink 

oxalic  acid  dyeing,  bleaching,  making  formic 

acid 

acetic  acid  white  lead  paint,  dyes,  and  medi- 

cines 

wood  alcohol  varnish,  solvent,  dyes,  denaturing 

alcohol,  fuel,  making  formalde- 
hyde, and  smokeless  powder 

acetone  explosives,  films,  dyes,  and  solvent 


THE  ECONOMIC  IMPORTANCE  OF  FORESTS        499 


1.  Timber  products. 


NOTES  ON  TABULATION 


(a)  U.  S.  produces  38,000,000  thousand  feet  of  "soft  wood"  lumber 

per  year,  and  8,000,000  thousand  feet  of  hard  wood  lumber. 

(b)  The  chief  kinds  are 

yellow  pine  from  Carolina,  Georgia,  etc.  (40  %). 
white  pine  from  Michigan,  Wisconsin,  Minnesota, 
spruce  and  redwood  from  the  Pacific  slope. 

(c)  The  enormous  number  of  trees  cut  may  be  judged  when  we  realize 

that  65  %  is  wasted  in  making  lumber. 


< 

Yellow  Finer 

(Including  the  Short 

)                     I 

L-                     2 

Billions  of 

( 

Board  Feet 

*                       4 

t                     S 

6 

Leaf  and  Loblolly 
fines) 

Oak 

UaK 
\Vh\ia  "Pi  -no 

\V  nite  .tine 
Hemlock 

Western  Pine 

—  — 

— 

Spruce 

— 

— 

Maple 

— 

Cypress 

—  — 

Tulip  Poplar 

•••••• 

Bed  Gum 

••Ml 

Redwood 

mmm 

Chestnut 

mmmm 

Beech 

mam 

Birch 

mmm 

Cedar 

mm 

Basswood 

mm 

Hickory 

mm 

Elm 

mm 

Larch 

mm 

Ash 

mm 

Cottonwood 

• 

White  Fir 

• 

Tamarack 

• 

Sugar  Pine 

• 

Tupelo 

• 

Balsam  Fir 

I 

Sycamore 

1 

Walnut 

1 

Lodgepole  Pine 

I 

All  Other 

• 

FIG.  158.    Lumber  production  by  varieties,  1910.    (U.  S.  Forest  Service.) 


500  BIOLOGY  FOR  BEGINNERS 

(d)  Railroads  use  2500  ties  per  mile  —  there  are  about  200,000 
miles  in  U.  S.  and  the  ties  have  to  be  replaced  every  seven 
years;  this  means  the  use  of  about  70,000,000  ties  per  year. 

2.  Paper.     A  single  New  York  daily  newspaper  uses  for  paper  the  spruce 

trees  from  44  acres  per  day. 

The  greatest  amount  of  paper  is  made  in  New  York,  Wisconsin,  and 
New  England. 

3.  Fuel.     Coal  is  indirectly  a  forest  product  as  it  is  the  carbon  from  trees 

of  ages  ago,  partly  decomposed  under  the  earth  by  heat  and 
pressure. 

4.  Naval  stores.     These  are  so  called  because  tar  and  pitch  are  used  in 

connection  with  ship  building  and  cordage.     The  crude  pitch  is 
obtained  by  notching  the  southern  pines  and  collecting  the  product - 
which  is  distilled,  making  tar,  turpentine,  and  rosin.     U.  S.  ex- 
ports seven  times  as  much  turpentine  and  ten  times  as  much  rosin 
as  any  other  country.     The  value  reaches  $36,000,000  per  year. 

5.  Tanning  materials.     Quebracho  and  other  tropical   woods  could  be 

included. 

6.  Maple  sugar.     U.  S.  produces  50,000,000  pounds  and  4,000,000  gallons 

of  syrup  per  year,  of  which  Vermont  and  New  York  supply  over 
three-quarters. 

7.  Spruce  gum.     This  gum  forms  in  masses  on  the  bark  of  spruces  and  is 

gathered  and  cleaned  in  the  winter.     Really  fine  gum  is  worth 
•  several  dollars  a  pound. 

8.  Distillation  products.     Various   kinds   of   hard   wood   are   heated   in 

closed  iron  cylinders,  destructive  distillation  goes  on,  charcoal 
remains  in  the  cylinders  and  the  other  products  go  off  as  vapors  and 
arq  condensed  and  separated.  We  will  learn  more  about  this  in 
chemistry.  For  the  present  notice  how  many  products  there  are. 
and  for  what  various  and  important  purposes  they  are  used. 


FOREST  ENEMIES 

Man.  Valuable  as  they  are,  forests  have  many  enemies,  and 
strange  as  it  may  seem,  one  of  the  worst  of  them  is  man.  Of 
course  we  destroy  much  standing  timber  for  necessary  use  and 
for  clearing  for  agriculture,  but  much  more  is  utterly  wasted  in 
other  ways.  Annual  growth  in  the  United  States  is  7,000,000,000 
feet  but  the  annual  consumption  totals  over  20,000,000,000  feet. 

Careless  lumbering,  in  which  only  a  few  trees  are  used  and  many 
destroyed,  or  wasteful  methods,  by  which  only  one-fourth  of  the 
cut  timber  ever  becomes  lumber,  are  some  of  man's  methods  of 
attack.  Cutting  hemlock  and  using  only  the  tan  bark,  leaving 


THE  ECONOMIC  IMPORTANCE  OF   FORESTS         501 

the  stripped  timber  a  total  loss  and  danger  in  case  of  fire,  is  an- 
other barbarous  waste  for  which  man  is  responsible.  . 

Fire  is  one  of  the  forests'  worst  foes  and  except  for  lightning, 
man  is  the  author  of  them  all.  Sparks  from  locomotives  and  camp 
fires  of  careless  hunters  account  for  some  which  start  accidentally, 
while  grazers  and  berry  pickers  start  fires  on  purpose  to  help  their 
crops,  and  men,  clearing  land,  often  lose  control  of  their  fires  and 
cause  great  destruction.  In  1915  there  were  40,000  fires,  covering 
6,000,000  acres,  or  over  1  per  cent  of  all  forests  in  United  States, 
which  caused  a  loss  of  $7,000,000  and  many  lives.  During  the 
same  year  2j  million  were  spent  for  forest  protection  or  only 
one-third  the  year's  loss. 

Insect  Enemies.  In  our  study  of  insects,  the  damage  which 
they  do  to  crops  was  mentioned,  and  the  forest  crops  are  no  ex- 
ception. The  saw  fly,  bark  beetles,  gyspy  moth,  tent  caterpillar, 
and  tussock  moth  are  some  of  the  most  harmful,  and,  unlike  the 
orchard  pests,  the  extent  of  the  forests  makes  spraying  impos- 
sible. The  birds  are  almost  our  sole  protection  against  these 
forest  enemies,  though  toads,  snakes,  and  ichneumon  flies  do 
their  share. 

Fungus  Enemies.  Whenever  we  see  a  shelf  fungus  on  a  tree 
we  may  be  sure  that  tree  is  doomed  unless  help  is  provided.  But 
the  most  damage  is  done  by  less  conspicuous  forms,  such  as  the 
rusts  and  blights,  of  which  the  chestnut  blight  is  a  notable  ex- 
ample. (Not  only  are  the  trees  destroyed  but  their  lumber  is 
ruined  by  fungi,  both  in  standing  timber  and  often  after  it  is  cut 
and  piled.) 

Weather  Conditions.  Despite  their  great  strength,  trees  often 
fall  victims  to  wind  and  snow,  and  in  many  regions  great,  strips 
are  blown  down  by  tornadoes  making  the  almost  impassable 
"  windfalls  "  which  later,  when  dead  and  dry,  furnish  ideal  fuel 
for  forest  fires.  Sleet  storms  destroy  many  buds  and  even  large 
branches,  especially  if  followed  by  severe  winds,  and  thus  damage 
or  kill  many  valuable  forest  trees. 

Grazing  Animals  and  Others.  Large  herds  of  cattle  or  sheep 
often  damage  forests  by  trampling  on  the  young  trees  and  by 


502  BIOLOGY  FOR  BEGINNERS 

feeding  on  the  limbs  and  leaves.  Mice,  porcupines,  and  rabbits 
often  girdle  the  trees  by  eating  their  bark,  and  some  little  damage 
is  done  by  birds  and  squirrels  which  eat  their  seeds. 


FOREST  PROTECTION 

The  value  of  the  forests  of  the  United  States  is  evidently  very 
great,  but  only  recently  have  efficient  means  been  taken  to  pro- 
tect them. 

Legal  Protection.  To  begin  with,  one  of  the  most  important 
means  of  protection  lies  in  the  hearty  cooperation  of  every  citizen 
in  observing  and  enforcing  the  present  forest  laws  as  to  fire  pre- 
vention and  proper  lumbering. 

Careful  Lumbering.  The  average  lumberman  harvests  his 
crop,  but  does  not  plant  another.  Hence  we  face  the  ever  rising 
cost  of  lumber,  whereas,  if  the  timber  annually  cut  is  regulated 
so  as  not  to  exceed  the  year's  growth  the  forest  will  continue  to 
produce  like  any  other  crop. 

Reforestation.  Another  means  of  protection  consists  in  re- 
planting, either  by  setting  out  small  trees,  or  cutting  only  mature 
ones  and  leaving  young  and  seed-bearing  trees  so  that  nature 
can  attend  to  the  replanting. 

Forest  Reserves.  The  Government  has  established  large  forest 
reserves  which  are  kept  by  the  Nation  to  protect  drainage  for 
irrigation,  to  supply  grazing  areas,  and  provide  timber  under 
supervised  cutting.  (See  p.  496.) 

Forest  Rangers.  To  protect  these  enormous  tracts  of  Govern- 
ment forest  from  fire  or  theft,  there  is  provided  a  body  of  expert 
Forest  Rangers  under  Government  control. 

These  men  patrol  the  forests,  report  and  prosecute  theft,  and 
organize  to  fight  forest  fires  before  they  may  get  out  of  control. 
This  work  has  saved  millions  of  dollars  and  many  lives  in  the  line 
of  fire  prevention  alone. 

Forestry  Schools.  Furthermore,  there  are  established  Forestry 
Schools  at  Cornell,  Michigan,  Syracuse,  Yale,  and  elsewhere,  in 
which  the  scientific  methods  of  lumbering,  planting,  and  pro- 


THE  ECONOMIC  IMPORTANCE  OF  FORESTS        503 

tection  are  taught.  For  those  unable  to  attend  these  institutions, 
many  bulletins  and  other  publications  are  available  from  state 
and  national  governments,  giving  valuable  information  regard- 
ing this  important  source  of  our  natural  wealth. 

The  farmer  who  would  cut  down  his  apple  trees  to  gather  the 
fruit,  or  who  harvested  a  crop  without  planting  another,  would 
be  considered  insane,  yet  the  treatment  of  our  forest  resources 
amounts  almost  to  this.  The  sooner  we  realize  the  fact  that  a 
forest  is  a  crop  to  be  tended  and  gathered,  planted,  and  protected 
like  any  other,  the  sooner  our  lumber,  paper,  and  other  products 
will  cease  to  increase  in  cost. 

TIMBER  STRUCTURE 

A  great  deal  of  the  value  of  lumber  depends  on  one  of  three 
factors,  its  durability,  strength,  or  appearance.  These  in  turn 
depend  upon  the  minute  structure  of  the  tree  stem  and  though 
this  was  discussed  in  Chapter  XI,  it  needs  to  be  recalled  in  this 
connection. 

A  woody  stem  is  made  up  of  wood  fibers  and  ducts  (tracheids 
in  the  evergreens).  These  are  arranged  in  annual  rings  caused 
by  larger  ducts  forming  in  the  spring,  and  fewer  and  smaller  ones 
in  autumn  and  winter. 

"  Grain."  Evidently  a  board  cut  from  such  a  stem  will  have 
alternate  layers  of  harder  and  softer  tissue  which  cause  the 
"  grain  "  seen  in  most  woods.  If  the  board  is  cut  from  near  the 
side  of  a  log,  few  annual  rings  will  show  on  the  surface,  their 
sides  will  be  exposed  for  wear  and  will  give  a  grain  figure  like 
(A).  If  the  board  be  cut  near  the  center  of  the  log  (B)  all  the 
annual  rings  will  show  and  their  edges  are  exposed  for  wear  which 
makes  the  lumber  more  durable  and  less  liable  to  sliver  up.  The 
former  (A)  is  known  as  "  bastard  sawed  "  and  the  latter  (B)  as 
"  rift  sawed  "  lumber.  As  a  log  is  cut  up,  the  first  boards  will 
be  bastard  grain,  then  as  the  center  is  approached,  more  and 
more  nearly  rift  grain,  and  finally  bastard  cut  after  the  center  is 
passed.  Obviously  there  are  more  bastard  than  rift  boards  and 
hence  the  latter  are  more  expensive,  as  well  as  more  durable. 


504 


BIOLOGY  FOR  BEGINNERS 


Quarter  Grain.  In  all  stems  there  are  pith  rays  extending  from 
pith  to  bark,  but  only  in  oak,  maple,  sycamore,  and  a  few  others 
are  they  large  enough  to  affect  the  grain  of  the  timber.  Since 
these  pith  rays  run  toward  the  bark,  a  board  cut  at  (C)  would 
show  only  their  cut  ends  which  would  be  too  small  to  notice, 
whereas,  if  the  board  be  cut  at  (D)  the  pith  rays  will  be  cut  more 
or  less  side  wise  and  will  show  as  the  plates  or  flakes  which  are 
characteristic  of  "  quartered  oak,"  giving  it  its  beauty  and  value. 

In  order  to  get  as  many  boards  as  possible  showing  this  flake 


.  FIG.  159.     Diagram  showing  cause  of  grain  in  timber  and  various 
methods  of  sawing  so  as  to  take  advantage  of  the  grain. 

grain  (side  of  pith  ray)  the  logs  are  sometimes  cut  in  quarters  and 
then  sawed  from  the  center  outwards  so  as  to  show  the  sides  of 
as  many  pith  rays  as  possible  —  hence  the  term  "  quarter  sawed  " 
or  "  quartered  oak."  The  bastard  cut  oak,  which  shows  only 
the  annual  ring  grain  (as  in  A)  is  sold  as  "  plain  "  oak  and  while 
almost  as  durable  is  not  nearly  as  handsome. 

Heart  and  Sap-wood.  As  a  tree  grows  larger,  only  the  outer 
annual  rings  carry  sap  in  their  ducts,  while  the  inner  region  be- 
comes practically  dead,  its  only  function  being  support.  This 


THE  ECONOMIC  IMPORTANCE  OF  FORESTS         505 

center  part  is  called  the  "  heart  wood  "  and  is  often  darker  in 
color  and  more  durable  than  the  outer,  live  region  or  "  sap-wood." 
The  heart  of  a  tree  may  totally  decay  and  yet  cause  the  tree  no 
harm  other  than  weakening  its  strength,  but  the  sap-wood  is  neces- 
sary to  the  growth  of  the  tree  and  may  even  keep  it  alive  when  the 
bark  has  been  girdled. 

Shrinkage  and  Warping.  Fresh-cut  timber  contains  much  water 
and  the  process  of  drying,  called  "  seasoning,"  has  to  be  thoroughly 
accomplished  before  it  can  be  used.  This  is  because  lumber 
shrinks  as  it  dries  and  no  amount  of  nailing  will  hold  poorly  sea- 
soned boards  together.  As  a  board  dries  there  is  a  tendency  for 
the  side  nearest  the  bark  to  shrink  fastest  causing  the  board 
to  curve  away  from  the  center,  or  "  warp."  Unless  the  lumber 
be  properly  piled  and  dried  it  may  be  rendered  unfit  for  use. 

Hard  and  Soft  Woods.  Trees  can  be  grouped  in  two  classes, 
those  with  broad  leaves,  which  are  shed  annually  (maple,  oak) 
and  those  with  needle-shaped  leaves,  which  are  not  all  shed  at 
one  time  (pine,  spruce).  The  former  produce  "  hard  wood" 
lumber  and  the  latter  "  soft  wood,"  though  some  broad-leaved 
trees  have  lumber  that  is  very  soft  (basswood,  willow)  and  some 
pines  produce  "  hard  pine  "  lumber,  which  nevertheless,  is  classed 
as  a  "  soft  wood." 

"  Knots  "  in  lumber  are  places  where  a  branch  has  been  broken 
off  and  the  scar  covered  by  additional  annual  rings.  If  the  wound 
healed  at  once  and  no  rot  commenced,  the  knot  is  tight  and  does 
not  harm  the  lumber  so  much,  but  if  the  healing  was  incomplete, 
a  loose  knot  results  and  a  knot-hole  in  the  board  is  the  result. 

A  tree  grows  in  height  only  at  the  tips  of  new  branches;  it  grows 
in  thickness  layer  by  layer,  over  all  parts,  hence  a  nail  driven  into 
a  tree  will  always  remain  at  the  same  height  from  the  ground,  but 
will  be  covered,  in  time,  by  the  growth  in  thickness. 

Street  Trees.  In  proportion  to  their  number,  trees  are  more 
valuable  in  the  city  than  in  the  forest.  Shade  trees  add  to  the 
cash  value  of  property  in  the  same  way  as  do  wide  streets,  good 
pavements,  and  favorable  location.  A  city  always  is  proud  of 
handsome  trees  and  shady  streets,  but  often  there  is  little  care 


506  BIOLOGY  FOR  BEGINNERS 

exercised  in  their  planting  or  maintenance.  If  quick  growth  and 
immediate  results  are  wanted,  soft  maples  or  poplars  are  used,  but 
these  are  short  lived  and  rather  easily  broken  by  storms.  Elms 
and  hard  maples,  on  the  other  hand,  grow  slowly,  but  are  sturdy 
and  live  to  great  age. 

City  trees  require  special  protection  as  they  are  especially 
valuable  and  are  not  living  under  natural  conditions.  Insect 
attacks  can  be  overcome  by  proper  spraying;  damage  by  horses 
and  traffic  can  be  prevented  by  guards  around  the  trunks;  suit- 
able laws  can  be  enforced  to  protect  from  damage  by  careless 
linemen  who  cut  out  the  tops  to  pass  their  wires;  sidewalks  and 
curbs  can  be  kept  from  injuring  the  roots;  and  "  surgical  "  treat- 
ment should  be  used  when  rot  or  injury  makes  wounds  in  any  part. 

COLLATERAL   READING 

Elementary  Studies  in  Botany,  Coulter,  pp.  419-431;  A  First  Book  of 
Forestry,  Roth,  entire;  Care  of  Trees,  Fernow,  entire;  Handbook  of  Trees, 
Hough,  look  through;  Nature  Study  and  Life,  Hodge,  pp.  365-391;  Prac- 
tical Biology,  Smallwood,  pp.  376-388;  Principles  of  American  Forestry, 
Green,  entire;  Trees  of  Northern  United  States,  Apgar,  look  through; 
Commerce  and  Industry,  Smith,  pp.  182-208;  Our  Native  Trees,  Keeler, 
look  through;  "American  Forestry"  a  monthly  periodical. 

SUMMARY 
Value  of  Forests. 

1.  Control  of  water  supply. 

2.  Benefit  to  soil,  humus. 

3.  Effect  on  climate,  wind  protection. 

4.  Home  for  birds  and  game. 

5.  Forest  products  (see  tabulation). 

Enemies  of  the  Forests. 

1.  Man,  through  careless  lumbering,  fires,  etc. 

2.  Insect  enemies. 

3.  Fungus  diseases. 

4.  Weather  conditions,  sleet,  frost,  snow. 

5.  Grazing  and  other  animals.     Rodents. 

Protection  of  Forests. 

1.  Laws,  enforced  and  supported  by  people. 

2.  Careful  lumbering. 

3.  Reforestation,  planting,  etc. 


THE  ECONOMIC  IMPORTANCE  OF  FORESTS        507 

4.  Forest  reserves  held  by  the  Government. 

5.  Forest  rangers  to  protect  reserves. 

6.  Forestry  schools,  to  instruct  people. 

Timber  Structure. 

1.  Grain,  due  to  annual  rings,  bastard  and  rift,  due  to  pith  rays, 

quarter  and  plain. 

2.  Heart  and  sap  wood. 

3.  Shrinkage  and  warping. 

4.  Hard  and  soft  woods. 

5.  Knots. 

Street  Trees. 

1.  Value. 

2.  Most  useful  kinds. 

3.  Means  of  protection. 


CHAPTER  LI 
TOBACCO   AND   TABLE  BEVERAGES 

Vocabulary 

Nicotine,  a  harmful  ingredient  of  tobacco,  an  alkaloid  narcotic. 

Acreolin,  an  irritating  substance  in  tobacco  smoke. 

Caffein,  an  alkaloid  found  in  tea,  coffee,  and  cocoa. 

Cocaine,  an  alkaloid  from  leaves  of  coca  plant.     No  connection 

with  cocoa. 
Morphine,  an  alkaloid  from  the  opium  poppy  juice. 

The  damage  done  by  alcohol  and  tobacco  are  often  dealt  with 
in  the  same  chapters  and  spoken  of  together,  as  if  they  had  much 
in  common.  This  is  unfortunate,  for  young  people,  seeing  men 
little  harmed  by  use  of  tobacco,  will  assume  that  alcohol  is  no 
worse,  and  come  to  very  wrong  conclusions. 

Tobacco  does  harm  enough,  wastes  resources  enough,  but  we 
ought  not  to  let  alcohol  assume  any  comparison  of  their  relative 
danger.  This  is  not  to  excuse  the  use  of  tobacco,  but  to  prevent 
young  persons  from  concluding  that  one  is  no  more  harmful  than 
the  other,  merely  because  they  are  often  spoken  of  together.  A 
comparison  of  this  chapter  with  the  one  on  alcohol  will  make  the 
matter  sufficiently  plain. 

Tobacco.  It  is  well  known  that  protoplasm  in  a  young  plant 
or  animal  is  more  easily  injured  than  when  it  has  attained  full 
growth.  The  seedling  plant  is  more  easily  killed  by  frost  or  heat; 
the  chick  is  harmed  by  exposure  that  would  not  be  felt  by  the  hen ; 
the  human  infant  is  injured  by  various  things  which  would  not 
affect  the  adult  at  all.  This  is  not  alone  because  of  the  deference 
in  size  of  body,  but  the  growing  active  protoplasm  is  much  more 
sensitive  than  when  it  reaches  maturity,  and  therefore  is  much 
more  seriously  affected  by  stimulants  and  narcotics. 

508     ' 


TOBACCO  AND  TABLE  BEVERAGES       509 

Herein  lies  the  chief  biologic  argument  against  the  use  of  to- 
bacco. Tobacco  contains  a  harmful  alkaloid,  nicotine,  and  also 
produces  when  burned,  carbon  monoxid,  which  is  a  poisonous  gas. 
In  addition  if  the  smoke  is  inhaled,  a  substance  called  acreolin, 
together  with  the  smoke  particles,  increases  the  irritating  effect. 

If  used  by  boys  who  have  not  attained  the  full  physical  ma- 
turity of  twenty  years  or  more,  these  substances  produce  numerous 
and  serious  results  which  should  at  least  postpone  the  use  of  to- 
bacco till  later  life. 

Tobacco  is  narcotic  in  effect;  narcotics  tend  to  decrease  bodily 
efficiency  and  hinder  growth.  The  physical  effects,  while  not  to 
be  compared  with  the  ravages  of  alcohol,  are  nevertheless  im- 
portant and  should  be  noted. 

Irritation  to  Mucous  Membranes.  Smoking  certainly  irritates 
throat  and  lungs,  especially  if  the  user  "  inhales."  This  opens 
the  way  for  germ  attack  in  addition  to  the  harm  done  to  the  tis- 
sues by  smoke  and  acreolin.  The  eyes  are  also  irritated  especially 
when  one  smokes  and  reads  at  the  same  time. 

Effect  on  Endurance.  Any  narcotic  interferes  with  nerve  con- 
trol, especially  of  heart  and  lungs.  That  this  is  the  case  with 
tobacco,  has  been  abundantly  proven  by  experiment.  For  this 
reason,  no  trainer  permits  smoking  by  members  of  his  team, 
knowing  well  that  endurance  and  "  wind  "  cannot  be  developed 
when  tobacco  is  used.  The  United  States  forbids  its  use  at  West 
Point  and  Annapolis  because  of  its  harmful  effects,  both  physical 
and  mental.  Figures  obtained  from  six  leading  colleges  show  that 
of  those  who  "  made  the  team  "  just  twice  as  many  were  non- 
smokers. 

Effect  on  Growth.  In  some  cases  the  use  of  tobacco  seriously 
affects  digestive  processes  and  in  its  early  use  the  stomach  usu- 
ally revolts  at  its  presence.  The  effect  of  excessive  smoking  may 
even  extend  to  the  vital  activities  of  protoplasm  and  actually 
"  stunt  the  growth  "  of  various  organs.  This  is  common  where 
it  is  used  when  very  young. 

Effect  on  Mental  Development.  Many  investigations  at  dif- 
ferent schools  and  colleges  have  thoroughly  proven  that  the  use 


510  BIOLOGY  FOR  BEGINNERS 

of  tobacco  affects  the  brain  enough  to  impair  scholarship. 
Dr.  Meylan,  physical  director  at  Columbia,  reaches  these  con- 
clusions: 

1.  Smokers  averaged  eight  months  behind  non-smokers  in  their 
advancement. 

2.  Scholarship  standing  of  smokers  was  distinctly  lower. 

3.  Use  of  tobacco  by  students  is  closely  associated  with  lack 
of  ambition,  application,  and  scholarship. 

Another  investigation  shows  that: 

1.  Smokers  average  lower  in  grades. 

2.  Smokers  graduate  older. 

3.  Smokers  grow  more  slowly  in  height  and  weight. 

4.  95  per  cent  of  honor  pupils  are  non-smokers. 

Dr.  Andrew  D.  White,  who  for  twenty  years  was  president  of 
Cornell  University,  says,  "  I  never  knew  a  student  to  smoke  ciga- 
rettes who  did  not  disappoint  expectations,  or  to  use  a  common 
expression  '  kinder  peter  out.'  I  consider  a  college  student  who 
smokes  as  actually  handicapping  himself  for  his  whole  future 
career."  Dr.  White  was  not  a  fanatic  and  used  tobacco  him- 
self after  he  reached  middle  life. 

In  spite  of  such  evidence  boys  certainly  will  note  many  success- 
ful men,  perhaps  their  own  fathers,  who  do  not  seem  to  be  harmed 
by  smoking,  and,  forgetting  the  difference  in  age,  will  draw  wrong 
conclusions.  Tobacco  would  do  less  harm  if  it  were  more  harm- 
ful, so  that  its  effects  could  be  .more  easily  traced. 

For  such  prospective  smokers  there  are  other  arguments. 

1.  Tobacco  certainly  becomes  a  "  habit."    Do  you  want  to  be 
"  held  "  by  a  useless  and  probably  harmful  drug? 

2.  Tobacco  is  offensive  to  many  people.    Are  you  so  selfish  as 
to  gratify  your  taste  to  the  discomfort  of  others? 

3.  Tobacco  decreases  your  personal  attractiveness.     The  odor 
of   breath,  hands,  and  perspiration,  the  stains   on   fingers   and 
teeth,  do  not  add  to  your  good  looks. 

4.  Tobacco  is  expensive.    A  regular-  smoker  spends  more  than 
he  realizes,  on  his  indulgence.     Don't  you  think  you  could  have 
more  fun  for  your  money? 


TOBACCO  AND  TABLE  BEVERAGES       511 

5.  The  growth  and  manufacture  of  tobacco  wastes  soil,  labor, 
and  money,  sorely  needed  in  productive  lines  of  industry. 

6.  Smokers  cause  about  one-fourth  of  the  fires,  both  in  buildings 
and  forests.    You  can  scarcely  find  a  factory  without  its  "  No 
Smoking  "  signs  on  this  account. 

To  quote  from  another  authority  in  conclusion: 

"  Whatever  difference  of  opinion  there  may  be  regarding  the 
effect  of  tobacco  on  adults,  there  is  complete  agreement  among 
those  best  qualified  to  know,  that  the  use  of  tobacco  is  in  a  high 
degree  harmful  to  children  and  youth." 

Tea  and  Coffee.  To  a  degree  much  less  than  tobacco,  these 
beverages  contain  an  alkaloid  called  caffein.  As  with  tobacco, 
their  use  is  certainly  not  wise  for  the  young.  With  adults,  mod- 
erate indulgence  may  do  no  harm  or  may  even  be  beneficial, 
though  this  is  a  matter  which  every  person  must  decide  for 
himself. 

Neither  has  much  food  value,  both  are  rather  costly,  and  both 
tend  to  become  habits.  On  the  other  hand  they  sometimes  seem 
to  soothe  the  nerves  (which  ought  not  to  need  soothing),  or  to 
permit  one  to  continue  work  when  nearly  tired  out,  which  also  is 
a  rather  doubtful  benefit. 

Cocoa  and  Chocolate  contain  less  caffein  and  a  great  deal  of  fat, 
hence  are  real  foods.  More  people  should  learn  to  properly  pre- 
pare them  and  then  tea  and  coffee  would  be  less  used,  with  benefit 
to  all  concerned. 

It  seems  almost  unnecessary  to  say  that  no  medicine  or  beverage 
containing  alcohol,  opium,  morphine,  chloral,  cocaine,  or  any  of 
their  derivatives  should  ever  be  used  except  by  advice  of  a  rep- 
utable physician.  The  awful  danger  of  forming  a  "  drug  habit  " 
in  this  way  has  led  to  stringent  laws,  which  we  should  all  help 
enforce. 


512  BIOLOGY  FOR  BEGINNERS 

TABULATION  OF  SOME  COMMON  DRUGS 


Stimulants 


Narcotics 


Alcohol,  slight  first  effect 

Caffein  in  tea,  coffee,  and  cocoa 

Strychnine 

Nux  vomica 

Gentian 

Quinine 


Alcohol,  general  effect 

Nicotine 

Opium,  morphine,  etc. 

Chloral 

Cocaine,  heroin,  etc. 

Codeine 


COLLATERAL   READING 

A  Handbook  of  Health,  Hutchinson,  pp.  89-93,  103-107;  The  Human 
Mechanism,  Hough  and  Sedgwick,  pp.  357-362,  377-379;  Applied  Biology, 
Bigelow,  pp.  551-553;  The  Next  Generation,  Jewett,  pp.  136-144;  Ap- 
plied Physiology,  Over  ton,  see  index;  General  Physiology,  Eddy,  see 
index;  Principles  of  Health  Control,  Walters,  see  index;  Civics  and  Health, 
Allen,  pp.  363-368;  Elementary  Biology,  Peabody  and  Hunt,  Ft.  II, 
pp.  75-81. 

SUMMARY 

1.  Comparison  of  alcohol  and  tobacco. 

2.  Tobacco.     Physical  objections  to  its  use. 

Sensitiveness  of  growing  protoplasm. 

Smoking  exposes  to  nicotine,  carbon  monoxide,  acreolin,  etc. 
General  narcotic  effect. 
Irritation  to  mucous  membranes. 
Reduces  endurance. 
Interferes  with  growth  and  digestion. 
Seriously  impairs  mental  development  and  scholarship. 
Social  objections  to  its  use. 
It  becomes  a  useless  habit. 
It  is  a  selfish  habit,  because  offensive  to  many. 
Decreases  personal  attractiveness,  odor,  stains,  etc. 
Unnecessary  expense. 

Wastes  soil,  labor,  and  money  in  its  production. 
Danger  in  causing  fires. 

3.  Tea  and  coffee. 

Contain  caffein. 

Very  slight  food  value. 

May  harm  digestion  or  nerves. 

Certainly  not  good  for  young  people. 

Unnecessary  expense. 


TOBACCO  AND  TABLE  BEVERAGES       513 


4.  Cocoa  and  chocolate. 

Contain  little  caffein  and  much  fat. 
Useful  as  foods. 

5.  Coco-cola  and  similar  drinks. 

May  contain  harmful  alkaloids. 
Seems  to  become  habitual. 
Expensive. 


ALCOH01 


CHAPTER  LII 

L  IN  RELATION  TO  BIOLOGY 
Vocabulary 


Magnitude,  size  or  importance. 
Detriment,  harm. 
Acceleration,  speeding  up  action. 
Excessive,  too  great. 
Morbid,  abnormal. 
Pre-disposition,  tendency  toward. 
Potent,  powerful. 
Therapeutics,  curative  medicine. 

The  chemist  would  say  that  "  alcohol "  is  one  of  a  number  of 
similar  compounds,  containing  carbon,  hydrogen,  and  oxygen  in 
the  proportions  C2HttO  and  would  insist  that  we  call  it  "  ethyl 
alcohol  "  or  "  grain  alcohol  "  to  distinguish  it  from  wood  alcohol, 
glycerine,  and  many  other  similar  forms.  The  physiologist  or 
physician  would  tell  us  that  it  is  a  narcotic  poison  in  its  action  on 
the  tissues,  disturbing  especially  the  nervous  system. 

The  reason  that  this  substance  demands  a  chapter  in  a  biology 
text  is  that  man,  from  the  earliest  times,  has  used  this  drug  be- 
cause of  its  intoxicant  effects,  until  now  its  bearing  upon  the 
development  of  the  human  race  has  become  one  of  the  greatest 
biological  problems. 

Alcoholic  beverages  may  be  classed  roughly  in  three  groups: 

1.  Beer  (2-5  per  cent  alcohol)  made  from  fermented  barley. 

2.  Wine  (15-20  per  cent  alcohol)  from  fermented  fruit  juices. 

3.  Whiskey  (30-50  per  cent  alcohol)  from  either  source,  but 
distilled  to  increase  its  strength. 

In  ancient  times  before  modern  methods  of  malting  and  dis- 
tilling were  invented,  wine  was  a  rare  and  comparatively  unim- 

514 


ALCOHOL  IN  RELATION  TO  BIOLOGY  515 

portant  drink,  but  now,  both  the  amounts  used  and  the  alcohol 
contained,  have  so  increased  that  alcoholic  liquors  are  a  biologi- 
cal question  of  the  first  magnitude.  In  the  discussion  that  follows 
it  must  not  be  forgotten  that  alcohol  is  an  indispensable  chemical 
substance,  used  as  a  solvent,  preservative,  and  raw  material  in 
numerous  industries.  These  are  matters  that  concern  the  manu- 
facturing chemist,  while  biology  has  to  do  only  with  its  effect 
when  used  as  a  beverage  by  man. 

Physical  Effects.  In  the  first  place  alcohol,  although  oxidized 
in  the  body,  cannot.be  classed  as  a  food,  yet  is  often  so  called  by 
people  who  should  know  better.  A  food  is  "  a  substance  which 
when  assimilated  in  the  animal  body  builds  tissue  or  produces 
energy  without  harming  the  organism."  Alcohol  harms  the 
organism  in  various  ways  as  will  be  shown,  hence  cannot  be  classed 
as  a  food. 

Alcohol  is  chiefly  oxidized  in  the  liver  and  the  heat  is  lost  by 
the  rush  of  blood  to  the  skin  (Atwater).  This  oxidation  produces 
uric  acid  which  overworks  the  liver  and  kidneys,  to  the  detriment 
of  both  (Beebe). 

Dr.  Irving  Fischer  of  Yale  says,  "  These  heat  values  cannot 
be  expended  without  at  the  same  time  poisoning  the  system  with 
alcohol,  so  it  is  not  even  technically  correct  to  count  the  heat 
value  of  alcohol  as  such." 

Dr.  Von  Bunge,  chemist  of  University  of  Basel  says,  "  Alcohol 
produces  energy  (heat)  but  increases  the  loss  of  heat  still  more; 
the  net  result  being  a  lowering  of  temperature;  the  feeling  of 
warmth  is  an  illusion  due  to  narcotic  action  on  the  nerves." 

The  same  authority  also  says,  "  Beer  does  contain  small  amounts 
of  dextrine  and  sugar  but  we  already  eat  too  much  of  these,  and 
supplied  by  beer,  they  are  fabulously  expensive  ;  beer  does  not 
promote  digestion." 

Despite  this  claim  that  alcohol  is  a  food,  no  one  really  thinks  of 
using  it  for  nourishment,  but  rather  because  of  its  narcotic  effects 
on  the  nerves.  Opium  and  phosphorus  are  also  oxidized  in  the 
body,  but  no  one  claims  food  value  for  these  poisons,  and  alcohol 
belongs  in  the  same  class. 


516  BIOLOGY  FOR  BEGINNERS 

Alcohol,  then,  is  not  a  food,  because 

1.  It  produces  a  net  loss  of  energy,  though  oxidized. 

2.  It  does  not  build  tissue,  but  poisons  it. 

3.  It  furnishes  its  small  apparent  energy  at  great  expense. 

Effect  on  Nutrition.  Alcohol  withdraws  water  from  all  food- 
stuffs and  acts  chemically  on  proteid,  exerting  a  hardening  action 
in  both  cases  and  hindering  the  work  of  the  digestive  fluids.  In 
the  same  way  it  hardens  and  irritates  the  tissues  lining  the  ali- 
mentary canal,  especially  the  walls  of  the  stomach,  where  it  al- 
ways interferes  with  normal  action,  and  may  cause  serious  disease. 
Alcohol  certainly  increases  the  flow  of  digestive  fluids  and  its 
medicinal  use  was  based  largely  on  this  effect  until  it  was  found 
that  the  abnormal  flow  caused  a  lack  of  fluids  later,  and  that 
glands  that  had  been  "  stimulated  "  by  alcohol,  refused  to  re- 
spond to  the  presence  of  mere  food. 

"  Acceleration  of  gastric  action  is  counter-balanced  by  inhibi- 
tory effect  of  alcohol  on  the  chemical  processes  of  digestion." 
—  Chittenden. 

The  direct  effect  of  alcohol  is  shown  most  plainly  in  its  action 
on  the  liver,  where,  as  already  mentioned,  it  overtaxes  and  irri- 
tates that  important  organ.  Over  60  per  cent  of  deaths  due  to 
cirrhosis  of  the  liver  are  cases  where  the  disease  was  caused  by 
alcoholic  liquors. 

Effect  on  Circulation.  The  chief  effect  of  even  small  amounts 
of  alcohol  is  to  paralyze  the  vaso-motor  nerves  which  control  the 
blood  flow  and  heart  action. 

Thus  with  relaxed  artery  walls  and  lessened  heart  regulation, 
the  pulse  is  quickened,  the  blood  is  driven  to  the  skin  and  mucous, 
membranes,  and  the  familiar  "  stimulant  "  effects  rare  poduced. 
Notice  in  the  first  place  that  this  is  due,  not  to  any  "  stimulation  " 
at  all,  but  to  a  deadening  of  the  nerve  controls,  and  second,  that, 
although  the  skin  feels  warm,  due  to  the  excess  blood,  it  is  actually 
losing  heat,  because  so  much  blood  has  been  brought  to  the  surface. 

"The  general  temperature  is  always  lowered." — Macey. 

Not  only  this,  but  with  continuous  use  alcohol  keeps  the  capil- 
laries relaxed,  causing  reddening  of  the  skin  and  inflammation  of 


ALCOHOL  IN  RELATION  TO  BIOLOGY  517 

the  mucous  linings,  both  of  which  favor  the  attacks  gf  various 
diseases. 

Alcohol  reduces  the  control  centers  and  so  the  circulatory 
organs  "run  away";  they  are  NOT  stimulated.  One  might  as 
well  talk  about  stimulating  a  steam  engine  by  removing  the  gov- 
ernor. Yet  this  is  a  very  common  error. 

Alcohol  is  never  a  stimulant,  but  always  a  narcotic,  producing 
its  results  by  its  interference  with  nerve  control  in  every  case. 
"  No  amount  of  alcohol,  however  given,  can  increase  the  amount 
of  work  done."  -  Dr.  Woodhead,  Cambridge  University. 

Aside  from  its  interference  with  the  normal  distribution  of  blood 
and  consequent  pre-disposition  to  colds  and  inflammations,  its  ex- 
cessive use  may  permanently  harden  the  arteries  (arteriosclerosis), 
or  affect  the  heart  muscles  (fatty  degeneration),  though  these  are 
not  so  important  from  a  biologic  standpoint  as  the  more  general 
effects  which  even  occasional  use  produces. 

Effect  on  Respiration.  The  interference  with  blood  regulation 
is  particularly  harmful  in  the  lungs,  causing  inflammation  and 
diminishing  resistance  to  pneumonia  and  congestive  diseases.  At 
the  same  time  connective  tissue  is  increased  and  the  actual  lung 
capacity  is  lessened.  A  curious  chemical  result  also  ensues; 
alcohol  is  so  easily  oxidized,  that  it  uses  oxygen  actually  needed 
to  release  the  energy  from  real  foods.  This  appears  to  be  a  "  stimu- 
lation "  of  the  breathing  process,  when  as  a  matter  of  fact,  the 
added  air  is  not  sufficient  to  oxidize  the  alcohol  alone.  The  final 
result  is  loss  of  energy  from  the  unoxidized  food  in  addition  to  the 
heat  wasted  by  way  of  the  skin,  as  shown  above. 

Effect  on  Excretion.  This  improper  oxidation,  and  interference 
with  blood  flow  and  skin  functions  produce  excess  of  uric  acid  and 
other  wastes  for  the  kidneys  to  dispose  of,  resulting  always  in 
impaired  function  and  sometimes  in  serious  disease.  Rheumatism, 
Bright's  disease,  and  fatty  degeneration  of  the  kidneys  may  be 
caused  or  encouraged  by  excessive  use  of  alcohol. 

Effect  on  Nervous  System.  As  has  been  shown,  alcohol's  prin- 
cipal line  of  attack  is  by  way  of  the  nervous  system  and  it  is  here 
that  its  effects  are  most  notable  and  most  serious.  In  the  evolu- 


518  BIOLOGY  FOR  BEGINNERS 

tion  of  the  nervous  system  the  centers  of  control  develop  in  this 
order: 

1.  Heart  and  circulation  control. 

2.  Respiration. 

3.  Walking  and  large  muscles. 

4.  Speech  and  other  senses. 

5.  Moral  and  intellectual  control. 

The  peculiar  harm  of  the  narcotic  action  of  alcohol  is,  that  it 
impairs  these  nerve  centers  in  reverse  order.  The  higher  emo- 
tions, moral  sense,  modesty,  judgment,  and  self-control  are  first 
attacked,  and  from  this  effect  arises  the  awful  record  of  alcohol 
as  a  cause  of  immorality  and  crime.  Leaving  the  body  control 
but  little  impaired  and  able  to  carry  out  the  impulses  of  a  dis- 
ordered mind,  a  man  will  commit  crimes  or  perform  acts  which  he 
never  would  have  thought  of  doing  if  his  self-control  had  not  been 
affected  by  this  dangerous  narcotic  drug.  Further  effects  of  al- 
cohol are  shown  when  the  speech  and  sight  centers  are  attacked, 
as  the  thick  speech  and  double  vision  of  the  alcoholic  victim  are 
all  too  familiar  evidence.  Next  the  walking  and  other  large  muscles 
are  affected  and  the  staggering  gait  and  uncertain  movements  are 
observed.  Finally,  the  breathing  is  interfered  with,  the  heart 
action  partially  or  wholly  paralyzed,  and  the  condition  of  "  dead 
drunkenness  "  or  even  death  ensues. 

If  the  order  of  its  effects  were  reversed,  alcohol  would  not  be 
so  dangerous,  because  the  body  would  then  be  unable  to  carry 
out  the  demands  of  the  deranged  brain.  Unfortunately,  this  is 
not  the  case,  and  herein  lies  one  of  alcohol's  greatest  biological 
dangers.  Furthermore,  alcohol  actually  attacks  the  brain  tissue, 
causing  irreparable  harm  and  producing  the  morbid  desire  for  more 
liquor  so  characteristic  of  the  victims  of  this  awful  habit.  The 
apparent  "  nerve  stimulation,"  so  frequently  mentioned,  is  merely 
the  paralysis  of  sense  and  self-control,  leaving  the  body  to  act,  often 
more  violently,  it  is  true,  but  never  increasing  its  effective  energy. 

"  Even  the  feeling  of  rest  due  to  slight  indulgence  in  alcohol  is 
caused  by  its  anaesthetic  effect  upon  the  sense  of  fatigue,  which 
is  the  safety  valve  of  the  human  machine." — Von  Bunge. 


ALCOHOL  IN  RELATION  TO  BIOLOGY  519 

The  whole  case  is  thus  summarized  by  Dr.  Brubacher  of 
Jefferson  Medical  College,  Philadelphia,  "  Alcohol  deranges  the 
activity  of  the  digestive  system,  lowers  the  body  temperature, 
impairs  muscular  power,  diminishes  the  capacity  for  mental 
work,  and  leads  to  actual  changes  in  the  tissues  of  the  brain 
and  other  organs." 

Alcohol  and  Disease.  Not  only  does  alcohol  have  the  specific 
effects  already  mentioned  but  injures  the  general  health  in  two 
ways: 

1 .  It  is  a  direct  cause  of  certain  diseases. 

2.  It  lowers  bodily  resistance  to  nearly  all  diseases. 
Examples  of  the  first  case  have  been  mentioned  in  connection 

with  the  various  organs,  such  as: 

Heart  diseases,  enlargement  or  fatty  degeneration. 

Inflammation  of  the  liver,  "  hobnailed  liver." 

Inflammation  of  the  stomach,  indigestion. 

Insanity. 

Far  more  important,  however,  is  the  effect  of  alcohol  in  lower- 
ing the  resistance  of  the  body  to  external  attack,  and  in  creating 
abnormal  internal  conditions,  which  make  the  course  of  many 
diseases  more  serious,  though  they  were  not  caused  by  the  use  of 
liquor. 
This  predisposition  to  disease  is  brought  about  in  two  ways: 

1.  The  white  corpuscles,  which  defend  us  against  bacterial  at- 
tack, are  destroyed,  and  the  ability  of  the  blood  to  provide  anti- 
toxins is  lessened. 

2.  By  the  various  disarrangements  of  nerve  control,  blood  and 
food  supply,   alcohol  overstrains   certain  organs,   and  interferes 
with  the  action  of  others,  so  that  diseased  conditions  are  produced. 

Statistics  compiled  by  the  Life  Insurance  Companies  of  the 
United  States  covering  a  period  of  twenty-five  years,  show  some 
remarkable  results,  as  follows:  More  than  twice  as  many  users  of 
liquor  died  of  pneumonia  as  abstainers,  the  ratio  being  18  to  39, 
and  Dr.  Osier  states  that  "  Alcohol  is  perhaps  the  most  potent  of 
all  predisposing  causes  of  pneumonia."  The  same  is  true  of  tuber- 
culosis, the  ratio  here  being  9.9  to  21.8:  that  is,  for  every  31.7 


520  BIOLOGY  FOR  BEGINNERS 

persons  who  died  of  the  disease,  21.8  were  drinkers,  and  only  9.9 
were  abstainers.  Or  to  put  it  still  another  way,  if  you  do  not  use 
alcohol,  your  chance  of  recovery  is  twice  as  good  as  though  you 
drank. 

Not  only  in  special  diseases  but  in  general  health,  the  insurance 
figures  show  the  harm  of  alcohol.  The  lives  of  "  light  drinkers  " 
are  shortened  an  average  of  four  years,  and  that  of  "  regular 
drinkers  "  six  and  a  half  years.  In  general,  the  death  rate  shows 
a  margin  of  26  per  cent  in  favor  of  the  non-user  of  alcohol.  Not 
only  is  the  life  shortened,  but  the  user  of  alcohol  is  ill  2.7  times 
as  often  as  the  abstainer,  and  his  illnesses  last  2.5  times  as  long; 
this  causes  not  only  discomfort  but  loss  of  work  and  money. 

We  have  spent  much  time  studying  the  prevention  of  typhoid 
and  smallpox  and  yet  alcohol  kills  more  people  than  typhoid  and 
fifteen  times  as  many  as  smallpox,  in  this  country  every  year. 
Perhaps  the  most  awful  item  in  this  catalog  of  the  effects  of  al- 
cohol on  the  human  organism  is  the  fact  that,  throughout  the 
United  States,  26  per  cent  of  the  inmates  of  our  insane  hospitals 
owe  their  condition  to  the  use  of  alcohol,  either  by  themselves  or 
their  parents. 

Mr.  Arthur  Hunter,  the  chief  actuary  of  the  New  York  Life 
Insurance  Company,  and  President  of  the  Actuaries  Society  of 
America,  from  whose  reports  many  of  these  facts  have  been  taken, 
sums  up  the  case  as  follows: 

"  In  my  judgment,  it  has  been  proven,  beyond  peradventure  of 
a  doubt,  that  total  abstinence  is  of  value  to  humanity;  it  is  certain 
that  abstainers  live  longer  than  persons  who  use  alcoholic 
beverages." 

Alcohol  is  not  a  Medicine.  In  this  connection  it  is  well  to  re- 
member that  alcoholic  beverages  are  no  longer  credited  with  any 
medicinal  value,  as  shown  by  the  following  resolution,  adopted  by 
the  American  Medical  Association,  June,  1917. 

"  Whereas,  we  believe  that  the  use  of  alcohol  as  a  beverage  is 
detrimental  to  the  human  economy;  and 

"  Whereas,  its  use  in  therapeutics,  as  a  tonic,  or  a  stimulant,  or 
a  food,  has  no  scientific  basis;  therefore  be  it 


ALCOHOL  IN  RELATION  TO  BIOLOGY  521 

"  Resolved,  that  the  American  Medical  Association  opposes  the 
use  of  alcohol  as  a  beverage;  and  be  it  further 

"  Resolved,  that  the  use  of  alcohol  as  a  therapeutic  agent  be 
discouraged." 

The  United  States  Pharmacopoeia,  the  accepted  guide  book 
of  medical  preparations,  was  revised  in  1917,  and  "  whiskey  " 
and  "  brandy  "  were  struck  out  from  its  lists,  which  are  supposed 
to  contain  all  the  useful  drugs;  "port  wine"  and  "sherry" 
were  left  out  several  years  ago.  Dr.  Harvey  Wiley,  perhaps  the 
most  celebrated  food  and  drug  chemist  in  this  country,  was  chair- 
man of  the  committee  which  made  these  changes.  The  present 
opinion  of  the  best  physicians  is  well  voiced  by  Dr.  J.  N.  Hurty, 
Secretary  of  the  Indiana  State  Board  of  Health.  He  says,  "  Al- 
cohol is  opposed  to  the  public  health,  for  it  hurts  any  animal 
organism  into  which  it  is  taken.  It  is  not  a  food;  it  does  not  aid 
digestion;  it  does  not  further  the  good  of  the  body;  on  the  con- 
trary, it  hurts." 

Alcohol  and  Efficiency.  Apart  from  its  disastrous  effect  of  health, 
the  results  of  the  use  of  liquor  on  actual  ability  to  do  work  must  be 
considered.  The  loss  of  labor  due  to  alcohol -caused  disease  equaled 
the  work  of  150,000  men  per  year  in  the  United  States  alone  under 
unrestricted  traffic.  Sobriety  will  increase  our  total  efficiency  as  a 
Nation,  from  ten  to  twenty  per  cent,  adding  to  the  country's 
wealth  over  two  billion  dollars  besides  what  would  have  been 
spent  for  the  liquor  itself.  To  balance  this  enormous  total,  the 
revenue  from  liquor  comes  to  less  than  half  a  billion. 

Waste  of  Resources.  Furthermore  there  is  great  waste  of  food 
stuffs  in  the  manufacture  of  liquor.  The  enormous  amounts  of 
corn,  barley,  rye,  and  fruits  can  ill  be  spared  when  the  cost  of 
living  is  so  high.  Coal  and  transportation  facilities  are  also  used 
by  the  liquor  business  to  a  very  great  extent.  Every  pint  of 
beer  wastes  a  pound  of  coal  to  make  it,  and  other  beverages  in 
similar  proportions,  to  say  nothing  of  the  rolling  stock  required  to 
transport  the  raw  materials  and  finished  product.  The  time  and 
skill  of  thousands  of  workmen  are  engaged  in  the  manufacture 
and  sale  of  liquors,  which  in  the  present  shortage  of  labor  in  es- 
sential industries  might  be  much  better  employed. 


522  BIOLOGY  FOR  BEGINNERS 

Since  writing  the  foregoing  chapter,  the  people  of  the  United 
States  have  added  to  our  Constitution  the  18th  amendment, 
prohibiting  the  manufacture  and  sale  of  alcoholic  beverages.  If 
this  is  properly  enforced,  most  of  the  awful  results  of  the  use  of 
alcohol  will  disappear.  It  is  to  be  hoped  that,  in  the  future,  a 
textbook  will  not  have  to  contain  a  chapter  on  the  evils  of  al- 
cohol, any  more  than  they  would  now  on  the  evils  of  negro  slavery. 

The  final  outlawing  of  the  liquor  traffic  can  be  attributed  mainly 
to 

The  long  campaign  of  education  as  to  its  harm. 

The  economic  waste  of  materials  and  labor. 

The  reduction  in  business  efficiency. 

The  physical  and  moral  effects. 

COLLATERAL   READING 

Alcohol  and  the  Human  Body,  Horsely  and  Sturge,  entire;  A  Handbook 
of  Health,  Hutchinson,  pp.  93-103;  Physiologic  Aspects  of  the  Liquor 
Problem,  Billings;  Elementary  Biology,  Peabody  and  Hunt,  Pt.  II,  pp.  64- 
75;  The  Human  Mechanism,  Hough  and  Sedgwick,  pp.  366-376;  The 
Next  Generation,  Jewett,  pp.  118-125,  145-152;  Applied  Physiology, 
Overton,  see  index;  General  Physiology,  Eddy,  see  index;  Principles  of 
Health  Control,  Walters,  pp.  130-153  and  index;  Civics  and  Health,  Allen, 
pp.  345-362;  Bulletins  of  the  Scientific  Temperance  Federation,  Boston; 
"Alcoholism"  in  Everybody's  Magazine,  1909;  The  Great  American  Fraud, 
American  Medical  Association,  Chicago. 

SUMMARY 
Introduction. 

Composition,  C2H6O.     "Ethyl"  or  "grain"  alcohol. 
Character,  narcotic  poison.     (Chloroform,  ether,  opium.) 
Reason  for  study  here.     Its  effect  as  a  beverage. 
Kinds  of  alcoholic  beverages. 

Beer,  2-5  %  alcohol,  made  from  malted  barley. 

Wine,  15-20  %  alcohol,  made  from  fruit  juices. 

Whiskey,  30-50  %  alcohol,  made  from  grains  or  fruits  (fermented  and 

distilled). 
Proper  uses  of  alcohol. 

Physical  Effects  of  Alcohol. 

I.   Alcohol  not  a  food,  because 

1.  Though  oxidized,  it  produces  a  net  loss  of  energy. 

2.  Does  not  build  tissue,  but  harms  it. 


ALCOHOL  IN  RELATION  TO  BIOLOGY  523 

II.  Effect  on  nutrition. 

1.  Makes  food  less  digestible  by 

(a)  Withdrawing  its  water. 
(&)  Hardening  its  proteid. 

2.  Action  on  digestive  organs. 

(a)  Irritates  all  membranes. 
(6)   Hardens  tissue  of  the  walls. 

(c)  Causes  abnormal  flow  of  fluids. 

(d)  Irritates  and  overworks  the  liver. 

III.  Effect  on  circulation. 

(a)  Interferes  with  nerve  control  of  heart,  etc. 

(b)  Relaxes  arteries  and  capillaries,  strains  heart. 

(c)  Blood  driven  to  skin,  temperature  lowered. 

(d)  Permanent  inflammation  of  internal  organs. 

(e)  Possible  cause  of  disease. 

IV.  Effect  on  respiration. 

(a)  Causes  inflammation  of  mucous  linings. 

(&)   Diminishes  resistance  to  congestive  diseases. 

(c)  Increases  connective  tissue,  lessening  lung  action. 

(d)  Robs  digested  food  of  oxygen. 

V.    Effect  on  excretions. 

(a)  Causes  excess  of  uric  acid. 
(6)  Overtaxes  the  kidneys. 

(c)   May    cause    disease,    rheumatism,    gout,    Bright's 
disease,  etc. 

VI.  Effect  on  nervous  system. 

(a)  Paralyzes  higher  centers  first. 

(6)  Later  loss  of  bodily  control. 

(c)  Actual  harm  to  nerve  tissues. 

(d)  Habit  formation.     Insanity. 

VII.  Alcohol  and  disease. 

0)  Direct  cause  of  heart  disease,  enlargement,  etc. 

Inflammation  of  liver  and  stomach. 

Insanity.     Arterio-sclerosis. 
(&)  Lowers  resistance  by 

(1)  Destruction  of  red  corpuscles. 

(2)  Predisposition  to  pneumonia,  tuberculosis,  etc. 

(3)  Affects  length  of  life,  illness,  etc. 
(c)    Alcohol  is  not  a  medicine. 

VIII.    Waste  of  resources. 
Foodstuffs. 
Coal. 

Transportation  facilities. 
Labor. 


CHAPTER  LIII 


SOME  GENERAL  BIOLOGIC  PROCESSES 


Liberate,  to  set  free. 
Accomplish,  bring  about. 
Petrified,  turned  to  stone. 


Vocabulary 


Osmosis  and  Life.  The  life  of  any  organism  depends,  first 
upon  getting  food  into  its  tissues,  and  second  upon  releasing  the 
energy  from  the  food  after  it  has  assimilated  it.  These  food- 
obtaining  processes  include  photosynthesis,  digestion,  absorption, 
and  assimilation.  All  these  depend  upon  osmosis  for  their  accom- 
plishment. 

After  the  food  is  available  in  the  body,  its  energy  must  be  re- 
leased. This  requires  oxidation  and  again  necessitates  osmosis 
for  the  passage  of  oxygen  through  the  tissues.  Oxidation  liberates 
the  energy  in  the  food  and  at  the  same  time  produces  waste  which 
must  be  excreted.  Here  again  osmosis  is  the  essential  process. 

The  tables  which  follow  attempt  to  show  this  relation  of  os- 
mosis to  the  vital  processes  of  all  plants  and  animals. 


ESSENTIALS  FOR  OSMOSIS 


In  plant 

In  apparatus 

Membrane 

Root  hair 
Epidermal  cell,  etc. 

Diffusion  shell 

Dense  liquid 

Cell  sap 
Protoplasm 

Sugar  solution 

Less  dense  liquid 

Soil  water 

Clear  water 

524 


SOME    GENERAL   BIOLOGIC   PROCESSES 


525 


OSMOTIC  PROCESSES  IN  PLANTS 
Absorption 


Soil  water 

Wnfrr               •     •• 

•*-> 

.S 

Cell  sap 

o 

^3 

ti 

Photosynthesis 

Air 

- 

Chlorophyll 
cells 

bearing 
icts 

>> 

n 

Sap 

Waf-rr 

1 

1 

a 

i 

C/J 

Transpiration 

Sap 

1 

crt 

"5 

Air  spaces 

M 

Transportation 

Sap 

s 

1 

Sap 

>t,  etc. 
mosis) 

s 

(successive  os 

Digestion 

Food  in  seed  or  root 

s 

u 

Embryo    or 
plant 

growing 

'II2 

OSMOTIC  PROCESSES  IN  ANIMALS 
Respiration 


Air  in  lungs 
Oxygen  — 


Blood 


Carbon  dioxide 
Water  vapor 
Nitrogenous  waste 


526 


BIOLOGY  FOR  BEGINNERS 

Digestion 


Food  in  digestive  tract  made  soluble  by 
ferments 

l|  '. 

U   ca    v 

Blood 

lyj 

^  S)^ 

"o  o  o                       > 

Assimilation 


Blood  and  lymph 

| 

.8  £ 

Tissues 

for  release  of 

3 

l! 

>  (Used 
energy) 

0    rt 

Excretion 


Urine  and  perspiration 

'a 

11 

Blood  in  kidneys  and 
skin 

E 

s  §* 

£3 

u 

^  'i 

Oxidation  and  Life.  In  the  process  of  photosynthesis,  plants 
accomplish  the  manufacture  of  organic  food  and  tissue  out  of  in- 
organic materials,  carbon  dioxide,  water,  and  mineral  salts. 
Plants  are  able  to  do  this  because,  by  means  of  their  chlorophyll, 
they  can  absorb  energy  from  the  sunlight  sufficient  to  unite  these 
inorganic  materials  into  complex  organic  substances. 

Animals  cannot  thus  manufacture  their  own  food,  as  they 
do  not  possess  chlorophyll.  It  is  evident  that  they  must  depend 
upon  plants  for  all  their  organic  food  substances.  Of  course  there 
are  animals  who  eat  no  plant  foods,  but  they  depend  upon  ani- 
mals which  do,  so  that  in  the  end  plants  are  the  only  food  pro- 
ducers. 

The  chief  function  of  food  is  to  provide  energy  to  support  the 
life  of  the  consumer.  This  energy  came  from  the  sun,  was  locked 


SOME  GENERAL  BIOLOGIC  PROCESSES  527 

up  in  the  food  substance  by  photosynthesis,  and  has  to  be  released 
or  set  free  by  oxidation.  Except  as  it  is  oxidized,  the  energy  in 
foods  or  fuels  cannot  be  released.  Hence  the  importance  of  oxi- 
dation as  the  key  which  unlocks  the  store  houses  of  solar  energy, 
and  makes  it  available  to  support  life.  We  do  not  know  how  the 
energy,  thus  released  by  oxidation,  produces  what  we  call  "  life," 
but  we  do  know,  that  without  it,  no  life  exists  and  that,  when 
oxidation  ceases,  life  ceases  too. 

Outside  of  living  energy  there  are  two  other  general  sources  which 
man  has  learned  to  use,  the  power  derived  from  fire  and  that  ob- 
tained from  water.  In  the  case  of  heat  energy  we  burn  (oxidize) 
various  fuels  such  as  wood,  coal,  gas,  or  oil.  All  these  fuels  are 
originally  derived  from  plant  life.  The  energy  which  we  set  free 
from  them,  therefore,  came  originally  from  the  sun.  Someone  has 
called  coal  "  petrified  sunshine";  this  is  almost  true.  When  we 
warm  our  hands  at  the  open  grate,  or  heat  our  house  with  coal, 
or  cook  with  gas,  or  light  our  rooms  with  electricity,  we  are  setting 
free  in  various  forms,  the  energy  absorbed  from  the  sun  by  plants. 

But  suppose  the  mill  is  run  or  the  electricity  used  is  generated 
by  water  power.  Here,  again  the  sun  is  the  final  source  because  its 
heat  has  evaporated  the  water,  which  has  risen  as  clouds,  fallen 
on  the  hills  as  rain,  and,  flowing  down  again  to  the  sea,  turns  the 
water  wheels.  To  be  sure  there  is  no  oxidation  involved  in  this 
process,  but  it  shows  how  the  sun,  either  by  its  light  or  its  heat, 
is  the  source  of  all  our  energy,  both  living  and  mechanical. 

Circles  in  Nature.  It  might  seem,  since  food  is  oxidized  or  fuel 
is  burned  to  release  its  energy,  that  the  supply  would  be  exhausted 
and  all  life  come  to  an  end.  Nature,  however,  works  in  circles, 
reclaims  all  waste,  and  aided  by  the  sun,  recombines  them  into 
useful  compounds  again. 

The  Carbon  Circle.  Carbon  is  one  of  the  most  necessary  ele- 
ments for  all  living  things.  Animals  obtain  it  from  plants  and 
plants  get  it  from  the  carbon  dioxide  of  the  air.  Plants  take  this 
carbon  dioxide  from  the  air,  combine  it  with  water  from  the  soil, 
and  lock  up  within  the  starch  which  is  formed  the  energy  of  the 
sun  which  formed  it. 


528 


BIOLOGY   FOR  BEGINNERS 


However,  the  carbon  is  not  lost.  When  either  plant  or  animal, 
fire  or  decay,  oxidize  these  plant  products,  carbon  dioxide  is  set 
free  again  in  the  same  amounts  as  before,  mixes  with  the  at- 
mosphere, and  is  ready  for  plant  use  again.  No  atom  of  carbon  has 
ever  been  destroyed  or  produced  by  life  processes;  it  is  merely 
used  over  and  over  again. 

The  Oxygen  Circle.     Oxygen  is  equally  important,  both  as 


5ALT5(Ca,  ria,  P,  Ft,n^,  5, 
NITRATES  .  NITRITES 


NH         CO       NITRATES 

'       PHOSPHATES 

OTHER  SALTS 


EARTH -"WATER 


FIG.  160.    Diagram  illustrating  the  cycle  of  living  matter  and  energy  in 
animals,  plants,  yeast  and  bacteria.    From  Calkins. 

being  a  part  of  all  living  tissue,  and  as  the  liberator  of  vital  energy. 
It  is  taken  from  the  air  whenever  plants  or  animals  breathe,  or 
wherever  fire  burns  or  substances  decay. 

All  these  processes  combine  the  oxygen  into  carbon  dioxide, 
water,  or  other  oxides,  and  one  might  suppose  that  it  was  per- 
manently removed  from  circulation,  but  this  is  not  the  case. 
Plants  take  this  carbon  dioxide  and  water,  unite  them  to  form 


SOME   GENERAL   BIOLOGIC   PROCESSES 


529 


starch,  set  free  in  the  air  the  oxygen  again,  and  thus  this  circle  is 
completed.  A  study  of  the  diagrams  will  help  to  fix  this  in  your 
mind. 

Nitrogen  Circle.  Nitrogen,  also,  is  absolutely  essential  to  all 
living  tissue  and  protoplasm  as  well  as  all  proteid  food.  Plants 
obtain  nitrogen  compounds  from  the  soil,  mainly  as  soluble  ni- 
trates. They  use  them  in  making  their  living  tissues,  which  in 
turn  furnish  to  animals  their  only  source  of  nitrogenous  food. 

Here  again  one  would  be  justified  in  supposing  that  the  nitro- 
gen was  out  of  reach  of  future  use.  If  this  were  so,  life  would  long 
since  have  ceased,  as  ordinary  soil  contains  only  enough  nitrogen 

CYCLE. 


mr 


ffforo  s Y/VTME  3  is 


FIG.  161.     Chart  showing  interdependence  of  plants  and  animals  for 
oxygen  and  carbon  dioxide. 

compounds  to  last  about  thirty  years,  if  none  were  replaced. 

All  waste  excreted  from  animals  contains  nitrogen  compounds, 
and  in  the  course  of  nature  this  should  get  back  to  the  soil  as 
natural  manures.  Whenever  a  plant  or  animal  dies,  decay  takes 
place,  and  much  of  its  nitrogen  is  thus  returned  by  the  action  of 
certain  decay  bacteria.  However,  neither  manures  nor  decay 
would  give  back  enough,  especially  as  man  disposes  of  all  his 
sewage  by  washing  it  into  rivers  or  ocean  where  it  cannot  get 
back  to  the  soil  from  which  it  came. 

Furthermore,  much  nitrogen  is  set  free  into  the  air  by  decay 
and  oxidation  in  such  a  way  that  plants  cannot  use  it,  except 
it  be  combined  with  other  elements.  So  there  would  be  a  serious 


530 


BIOLOGY  FOR  BEGINNERS 


shortage  if  it  were  not  for  other  means  of  return.  It  remains  for 
certain  bacteria,  living  in  the  nodules  which  they  form  on  the 
roots  of  clover,  peas,  beans,  alfalfa,  and  all  members  of  this  large 
family  of  plants,  to  aid  in  making  good  the  loss. 

These  bacteria  take  the  free  nitrogen  from  the  air,  combine  it 
into  soluble  compounds,  and  thus  replace  in  the  soil  most  of  this 
essential  element,  which  decay  and  oxidation  had  set  free  in  the  air. 


CYCLE. 


FIG.  162.  Diagram  showing  how  nitrogen  compounds,  after  being  used 
by  plants  and  animals,  are  either  returned  to  the  soil  by  decay,  or  reclaimed 
from  the  air.  This  completes  the  "nitrogen  cycle." 

Although  the  atmosphere  contains  an  enormous  amount  (80  per 
cent)  of  nitrogen,  it  is  not  in  the  form  of  compounds,  and  these 
plants  of  the  pea  family  are  the  only  ones  that  can  use  free  nitrogen. 

Another  means  by  which  free  nitrogen  of  the  air  is  combined 
into  useful  compounds  is  by  the  action  of  lightning,  which  con- 
verts some  into  oxides.  These  are  washed  back  to  the  soil  by  rain 
and  help  in  completing  the  circle. 

In  addition  to  these  natural  steps  in  the  nitrogen  circle  we  must 


SOME   GENERAL  BIOLOGIC  PROCESSES  531 

remember  that  man  has  learned  to  use  the  energy  of  nitrogen 
compounds  in  all  his  explosives  and  many  other  chemicals.  This 
interferes  seriously  with  nature's  plan,  for  the  firing  of  one  twelve- 
inch  gun  wastes  nitrogen  enough  to  raise  one  hundred  bushels  of 
wheat.  To  repair  this  loss  we  are  just  learning  to  artificially 
combine  the  nitrogen  of  the  air  into  useful  compounds,  and  replace 
them  in  the  soil  as  fertilizers.  Unless  this  is  done,  the  end  of  the 
nitrogen  supply  is  in  sight,  due,  as  usual,  to  man's  interference  in 
nature's  processes.  He  wastes  nitrogen  as  sewage,  chemicals, 
and  explosives,  so  must  do  his  part  in  completing  the  circle  or 
suffer  the  consequences. 


NITROGEN    IN    THE    SOIL 

Removed  by  Replaced  by 

Life  processes  •     Manures 

Decay  (some  kinds)  Decay 

Oxidation  of  useful  forms  Bacteria 

Waste  of  sewage  Electrical  action 

Industrial  uses  Artificial  processes 

Explosives  Fertilizers 

Other  Elements.  The  circles  which  are  followed  by  the  other 
elements  found  in  plant  and  animal  tissue  are  not  so  complicated. 
Hydrogen  comes  and  goes  as  water,  of  which  there  is  a  limitless 
supply  in  most  regions.  The  sulphur,  phosphorous,  potassium, 
and  other  mineral  compounds  are  usually  abundant  to  begin  with, 
and  are  not  set  free  by  decay,  but  come  back  to  the  soil  in  usable 
form. 

If  a  soil  becomes  deficient  in  any  of  these,  they  are  obtained 
elsewhere  as  natural  mineral  deposits  and  replaced  as  artificial 
fertilizer.  In  a  state  of  nature  this  would  never  be  necessary,  as 
the  plants  would  die  and  decay  where  they  grew  and  so  return  their 
mineral  salts  to  the  soil  that  produced  them.  It  is  only  when  man 
removes  his  crops,  and  uses  them  elsewhere,  that  artificial  re- 
placement is  necessary. 


532 


BIOLOGY  FOR  BEGINNERS 


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534  BIOLOGY  FOR  BEGINNERS 

Evolution  of  Life  Functions.  Biology  teaches  that  all  living 
things  are  alike  in  their  fundamental  life  processes,  that  all  forms 
are  related  by  descent  from  common  ancestors;  that  as  develop- 
ment proceeds,  they  become  better  fitted  to  perform  their  life 
functions,  or  in  other  words,  become  more  highly  specialized. 

The  accompanying  tables  are  intended  to  summarize  this  de- 
velopment in  life  processes,  as  shown  in  the  forms  which  we  have 
studied.  It  is  necessarily  much  condensed,  but  careful  study  will 
reveal  many  of  the  facts  brought  out  during  the  course. 

COLLATERAL   READING 

Osmosis:  Fundamentals  of  Botany,  Gager,  pp.  54-60;  The  Living 
Plant,  Ganong,  pp.  165-179;  Principles  of  Botany,  Bergen  and  Davis, 
pp.  36-39;  Introduction  to  Botany,  Stevens,  pp.  35-39;  Plant  Physiology, 
Duggar,  pp.  64-83;  Textbook  of  Botany,  Coulter,  Vol.  I,  pp.  302-309; 
Applied  Biology,  Bigelow,  pp.  85-97;  Elementary  Biology,  Peabody  and 
Hunt,  pp.  32-38;  The  Science  of  Plant  Life,  Transeau,  pp.  166-178;  General 
Physiology,  Eddy,  pp.  136-142;  College  Botany,  Atkinson,  pp.  13-21. 


SUMMARY 

1.  Osmosis  in  life  processes  (tabulated  in  text). 

2.  Oxidation,  the  release  of  energy. 

Plants  the  ultimate  source  of  food. 
The  sun  the  ultimate  source  of  energy. 

3.  Circles  in  nature. 

(a)  The  carbon  circle  (see  diagram). 

(b)  The  oxygen  circle  (see  diagrams). 

(c)  The  nitrogen  circle  (see  diagrams). 

(d)  Other  elements. 

4.  Evolution  of  life  functions  (tabulated  in  text). 


CHAPTER  LIV 

THE  HISTORICAL  DEVELOPMENT   OF  BIOLOGY 

Vocabulary 

Spontaneous,  without  cause. 

Mortality,  death  rate. 

Enumerate,  to  make  a  list  of,  to  number. 

Rabies  or  hydrophobia,  the  disease  caused  by  mad  dog  bite. 

Virulence,  disease  producing  ability. 

Like  all  other  sciences,  biology  has  developed  from  small  be- 
ginnings, by  the  labor,  study,  and  sacrifice  of  many  men  over  a 
long  period  of  years.  Biology  might  be  said  to  have  started  when 
man  first  became  intelligent  enough  to  observe  the  plants  and 
animals  with  which  he  was  surrounded,  and  utilize  or  avoid  them 
as  he  found  best. 

HARD  WON  KNOWLEDGE 

Circulation.  We  gain  our  present  knowledge  so  easily  and 
take  it  so  much  for  granted  that  we  can  hardly  realize  the  struggles 
by  which  even  our  simplest  facts  were  obtained. 

Every  child  knows  that  the  blood  circulates  in  the  arteries, 
but  the  ancients  believed  that  they  were  air  tubes  and  it  was 
only  in  1603,  after  much  opposition,  that  Harvey  was  able  to 
fully  prove  this  fact  of  circulation. 

Spontaneous  Generation.  We  assume,  as  a  matter  of  course, 
that  any  plant  or  animal  springs  from  a  parent  like  itself,  but  up 
to  1668  it  was  believed  that  maggots  came  from  decayed  meat, 
that  frogs  came  from  mud,  and  that  living  things  were  produced 
from  non-living  matter.  At  that  date  Redi  discovered  flies'  eggs 
and  larvae  and  proved  that  the  maggots  were  produced  by  flies. 
The  presence  of  bacteria  in  decaying  substances  was  not  explained 

until  1850-70. 

535 


536  BIOLOGY  FOR  BEGINNERS 

At  that  time  Pasteur  and  Tyndall  showed  that  bacteria  would 
not  develop  except  when  the  medium  had  been  exposed,  and  so 
proved,  even  for  these  minute  plants,  that  bacteria  were  produced 
by  bacteria,  and  in  no  other  way. 

The  idea  that  life  could  come  from  dead  matter  was  called  the 


FIG.  163.    William  Harvey.     1578-1667.    From  Locy. 

theory  of  "  spontaneous  generation,"  and  died  hard.    This  is  now 
replaced  by  the  belief  that  "  all  life  comes  from  life." 

Oxidation.    We  talk  freely  of  oxygen  and  oxidation,  but  oxygen 
was  not  discovered  until  1774  when  Priestley  obtained  it  and 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY     537 

demonstrated  some  of  its  properties.  Even  then  scientists  be- 
lieved that  when  a  substance  burned  it  gave  off  something  in- 
stead of  combining  with  something  (oxygen)  as  we  now  know  to 
be  the  case. 

Vaccination.  All  of  us  are  vaccinated  and  think  nothing  of  it, 
but  before  1796,  smallpox  raged  unchecked  and  was  so  common 
that  about  95  per  cent  of  all  people  had  it.  We  little  realize  the 
struggle  of  Dr.  Edward  Jenner,  an  English  physician,  who  was 
the  first  to  suggest  vaccination  as  its  cure. 

He  observed  that  the  dairy  maids  who  had  had  cow  pox  (a 
mild  form  of  smallpox)  did  not  fall  prey  to  the  latter  disease. 
Reasoning  from  this  he  proposed  to  inoculate  people  with  cow- 
pox  as  a  protective  measure,  and  suffered  ridicule,  opposition, 
and  persecution  before  he  could  convince  the  public.  Even  now 
there  are  a  few  misguided  individuals  who  oppose  vaccination, 
even  though  its  practice  has  made  smallpox  one  of  the  rarest  of 
diseases. 

DEVELOPMENT  OF  BIOLOGY 

It  would  be  impossible  to  enumerate  here  all  the  famous  names 
in  biology  or  to  sketch  their  contributions  to  our  knowledge. 
Only  a  few  can  be  mentioned,  but  there  are  books,  like  "  Bi- 
ology and  its  Makers  "  by  Locy,  which  deal  with  the  subject  in 
fascinating  style  and  treat  of  all  the  important  discoverers. 

A  few  of  these  are  listed  in  the  tabulation  at  the  end  of  this 
chapter,  and  a  glance  at  it  will  show  two  things,  —  how  old  some 
of  our  biologic  ideas  are,  and  how  young  is  our  definite  knowledge 
sufficient  to  apply  them.  The  Greeks  theorized  vaguely  about 
evolution  and  development,  but  it  was  over  two  thousand  years 
before  Darwin  and  others  proved  it.  Galen  was  the  foremost 
physician  of  his  time,  but  modern  medicine  scarcely  had  its  be- 
ginnings till  fifteen  hundred  years  later. 

Cells  and  Protoplasm.  Hooke  saw  cell  walls  in  cork  bark  in 
1671,  but  it  was  nearly  two  hundred  years  before  the  importance 
of  the  cell  as  a  unit  of  tissue  structure  was  proven  by  Schleiden 
and  Schwann  in  1838-39.  Both  Schleiden  and  Schwanri  noticed 


538  BIOLOGY  FOR  BEGINNERS 

the  jelly-like  substance  in  the  cells  but  it  was  not  until  1846  that 
von  Mohl  called  it  "protoplasm"  and  fifteen  years  later,  1861, 
Schultze  showed  that  it  was  the  fundamental  material  of  both 
plants  and  animals. 

Louis  Pasteur.  Probably  no  one  has  applied  biology  to  benefit 
mankind  to  a  greater  degree  than  Louis  Pasteur,  born  in  France 
in  1822:  died  1895,  "  the  most  perfect  man  in  the  realm  of 
science."  In  1857  he  showed  the  relation  of  bacteria  to  fermenta- 
tion and  greatly  benefited  the  wine  industry  of  France  by  his 


FIG.  164.  The  earliest  known  picture  of  cells  from 
Hooke's  Micrographia  (1665).  Edition  of  1780. 
From  Locy. 

investigations.  In  1865-68  a  disease  attacked  the  silk  worms  of 
France  and  Italy  and  threatened  to  wipe  out  the  industry. 
Pasteur  traced  this  to  bacterial  attack,  and  was  able  to  suggest 
means  by  which  the  silk  business  was  saved. 

Later  his  attention  was  turned  to  chicken  cholera  and  other 
animal  diseases  and  from  his  researches  along  these  lines  he  de- 
veloped the  treatment  by  inoculation,  and  laid  the  foundation 
for  all  modern  serum  and  anti-toxin  treatments. 

His  most  famous  work  was  done  in  the  treatment  of  rabies, 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY     539 

which  consists  in  injecting  weak  doses  of  the  hydrophobia  germs 
into  the  blood  of  a  person  bitten  by  a  mad  dog.  By  gradually  in- 
creasing the  virulence  of  the  injections  anti-toxins  are  built  up 
in  the  patient's  body  and  resist  the  real  attack  of  the  disease. 
By  this  treatment  the  mortality  has  been  decreased  from  practically 
certain  death  to  less  than  one  per  cent. 

The  world  owes  to  Pasteur  the  foundation  of  all  our  modern 
methods  in  bacteriology,  our  serum  and  anti-toxin  treatments, 
and  all  the  lives  that  have  been  saved  thereby.  Possibly  more 
people  owe  their  lives  to  the  results  of  his  work  than  to  that  of 
any  other  man  who  ever  lived. 

Other  Victories  over  Disease.  At  the  Pasteur  Institute  many 
discoveries  have  been  made  in  the  line  of  inoculation  against  lock- 
jaw (tetanus),  bubonic  plague  and  other  germ  diseases,  but  none 
has  saved  more  lives  than  the  anti- toxin  for  diphtheria.  This 
was  developed  by  Roux,  a  fellow  worker  with  Pasteur  and  by 
von  Behring,  a  German  bacteriologist  in  1894.  By  this  use  a 
disease  which  annually  caused  the  death  of  thousands  of  children, 
now  has  its  rate  reduced  about  80  per  cent  and  if  treatment  is 
given  early  in  the  case,  recovery  is  almost  certain. 

Among  others  who  have  labored  in  the  work  against  germ 
disease  may  be  mentioned  Robert  Koch,  who  studied  the  relation 
of  bacteria  to  human  disease,  especially  in  the  case  of  tuberculosis 
and  Asiatic  cholera.  He  was  the  first  to  identify  these  bacteria 
and  though  he  devoted  his  life  to  the  work,  did  not  discover  a 
specific  cure  for  tuberculosis.  However,  his  work  has  enabled  us 
to  take  preventive  measures  which  are  greatly  aiding  in  suppres- 
sion of  this  worst  of  the  "  ills  that  flesh  is  heir  to." 

Antiseptic  and  Aseptic  Surgery.  Sir  Joseph  Lister,  an  English 
surgeon,  was  the  first  to  fight  the  germs  of  the  operating  room  by 
the  use  of  antiseptics,  such  as  carbolic  acid.  This  one  discovery 
has  done  more  to  prevent  death  by  infection  after  operations 
than  any  other  of  recent  times.  Modern  surgery  aims  to  keep 
its  wounds  aseptic,  that  is,  free  from  all  germs  by  careful  methods 
of  sterilization,  but  still  relies  on  anti-septics  to  kill  any  germs  that 
may  have  found  entrance.  Before  Lister's  time  infection  of  op- 


540  BIOLOGY  FOR  BEGINNERS 

erative  wounds  was  to  be  expected  —  now  it  would  be  considered 
evidence  of  gross  carelessness  and  very  rarely  occurs. 

Among  other  names  to  be  associated  with  modern  advance 
against  disease  is  that  of  Paul  Ehrlich.  He  is  famous  for  his  study 
of  the  blood  as  related  to  immunity  to  certain  diseases,  and  es- 


FIG.  165.     Sir  Joseph  Lister.     1827-1912.     From  Locy. 

pecially  because  of  his  successful  method  of  treating  syphilis, 
which  before  had  been  incurable. 

Another  scientist  who  worked  along  similar  lines  was  the  Russian, 
Metchnikoff,  who  was  the  first  to  discover  the  functions  of  the 
white  corpuscles  in  combating  disease  germs  in  the  blood. 

Carrell  and  Flexner  are  two  American  scientists  who  are  work- 
ing at  the  present  time  to  carry  the  fight  against  disease  to  a  more 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY     541 

successful  conclusion.  Among  many  other  discoveries,  Carrell 
has  developed  a  very  successful  method  of  treating  infected  wounds 
which  saved  thousands  of  lives  during  the  war.  Flexner  has  been 
investigating  anti-toxin  treatments  for  infantile  paralysis  and 
similar  diseases. 

Charles  Darwin.    If  applied  biology  owes  its  greatest  debt  to 
Pasteur  and  his  successors,   certainly   theoretical  biology  owes 


FIG.  166.    Thomas  Henry  Huxley. 
From  Locy. 


1825-1895. 


more  to  Charles  Darwin  and  his  co-workers  than  to  any  other 
man.  His  work  along  the  line  of  evolution  and  natural  selection 
revolutionized  all  modern  thought  and  has  been  briefly  described 
in  Chapters  34  and  35. 

Associated  with  him  was  Alfred  Russell  Wallace  who  reached 
the  same  conclusions  as  Darwin,  though  working  from  different 
facts  and  entirely  independent  of  his  ideas. 


542 


BIOLOGY  FOR  BEGINNERS 


Huxley,  another  English  scientist,  defended  and  explained  Dar- 
win's theories,  and  Herbert  Spencer,  also  English,  applied  them 
to  all  lines  of  scientific  thought.  Upon  the  foundation  laid  by  these 
men,  all  modern  biology  is  based. 

Mendel's  Law  of  Inheritance.    In  1860  an  Austrian  priest,  by 


FIG.  167.    Gregor  Mendel.     1822-1884.    Permission  of  Professor  Bateson. 
From  Locy. 

the  name  of  Gregor  Mendel,  began  raising  peas  in  his  garden  at 
Brim.  He  was  not  so  much  interested  in  the  flowers  or  the  abun- 
dance of  the  crop  as  in  other  apparently  less  important  matters. 
He  noted  the  shape  of  seed,  and  their  color,  —  the  shape  and 
color  of  the  pods,  —  the  height  of  the  plant  and  other  similar 
characteristics.  He  kept  each  kind  separate  and  cross-pollenated 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY     543 

them  himself,  so  knew  exactly  the  ancestry  of  each  new  set  of 
descendants.  After  years  of  patient  experiment  and  careful  record 
he  reached  some  conclusions.  He  found  that  if  he  crossed  tall 
with  short  that  the  next  generation  were  hybrids  but  tall  in  ap- 
pearance, —  that  is,  tallness  had  overcome  shortness  as  a  char- 
acteristic in  that  generation. 

Many  characteristics  were  found  to  be  stronger  at  first  and 
were  called  "  dominant "  characteristics.  Those  which  were 
crowded  out  were  called  "  recessive."  However  when  these 


O 


P» 


FIG.  168.  Diagram  to  show  the  segregation  and  re-combination  of  the 
factors  (black  and  white)  in  the  gametes,  and  the  presence  of  both  in  the  hybrid 
F'.  (From  Morgan,  see  Calkins.) 


hybrids  were  bred  together  both  the  original  characteristics  re- 
appeared in  a  constant  proportion  of  tall,  short,  and  tall  hybrids. 

The  reason  is  that  the  two  characteristics  remained  separate 
in  the  hybrids  and  did  not  blend,  hence  when  hybrid  was  bred  with 
hybrid  the  next  generation  would  combine  these  characteristics 
according  to  the  mathematical  law  of  probabilities  or  chance. 

To  illustrate,  let  x  and  y  stand  for  any  two  non-blending  char- 
acteristics. The  first  crossing  would  produce  hybrid  offspring 
having  xy  characteristics,  but  if  x  were  dominant,  y  would  not 
appear. 


544  BIOLOGY  FOR  BEGINNERS 

However  if  these  xy  hybrids  are  crossed  together,  four  possible 
combinations  may  occur,  thus: 

Joining  x  with  x  producing  xx  offspring. 
"       x    "     y         "         xy 

"       y    "     x         "         yx        " 

"          y      "       y  "  yy  " 

Of  course  the  xy  and  yx  individuals  are  of  the  same  kind  and 
are  also  like  their  xy  hybrid  parents,  but  the  xx  and  yy  offspring 
have  those  characteristics  only  and  are  pure  bred:  their  off- 
spring with  either  x  or  y  respectively  would  produce  pure  x  or 
pure  y  characteristics,  despite  their  mixed  ancestry. 

Of  course  breeding  is  not  so  simple  as  this,  because  it  cannot  be 
limited  to  one  characteristic  at  a  time,  and  some  characteristics 
do  blend  or  average  in  the  hybrids,  but  the  law  of  inheritance, 
known  as  Mendel's  Law,  has  been  proven  true  and  is  of  great 
value  in  plant  and  animal  breeding. 

Though  Mendel  published  his  conclusions  in  1865  and  1869 
little  notice  was  taken  of  them  and  he  died  in  1884  without  recog- 
nition. Later  the  same  conclusions  were  independently  reached 
by  three  other  scientists  who  would  have  been  credited  with  an 
important  discovery,  but  in  1900  Mendel's  papers  were  found  and 
his  long  delayed  appreciation  arrived,  sixteen  years  after  his 
death. 

Briefly  stated,  his  law  comprises  three  facts: 

1.  Pure  bred  mated  with  pure  bred  of  same  kind  give  offspring 
pure  bred. 

2.  Pure  bred  mated  with  pure  bred  of  different  kind,  —  hybrid 
offspring. 

3.  Hybrid  mated  with  hybrid  the   offspring  will  be  one-half 
hybrid,  one-quarter  pure  bred  like  grandfather,  one -quarter  pure 
bred  like  grandmother. 

Law  I.  Pure  bred  with  pure  bred  of  same  kind,  x  plus  x  makes 
xx. 

Law  II.  Pure  bred  with  pure  bred  of  different  kind,  x  plus  y 
makes  xy. 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY    545 

Law  III.  Hybrid  bred  with  hybrid,  xy  plus  xy  makes  xx,  -\-2xy, 
+yy  or  stated  differently. 

xy .  .  xy  x         y hybrid 

t\  >"' 


i 

*" y. hybrid 


xx        xy_ yx_        yy  xx       xy 

2  xy  yx yy 

xx       2xy  yy 

Luther  Burbank.  No  one  has  made  such  successful  applica- 
tion of  these  laws  of  inheritance  as  has  Luther  Burbank.  For 
years  he  has  been  performing  what  might  be  called  biologic  miracles, 
on  his  farm  in  Southern  California. 

A  complete  list  of  the  new  or  improved  plants  which  he  has  de- 
veloped, would  occupy  a  whole  chapter,  but  some  of  the  most 
famous  are 

1.  The  Burbank  potato  which  has  increased  our  crop  by  mil- 
lions of  dollars  and  is  said  to  have  prevented  the  potato  famine 
that  formerly  devastated  Ireland. 

2.  The  spineless  cactus  which  provides  abundant  stock  food 
for  regions  where  none  was  to  be  had. 

3.  The  "  Primus  Berry,"  a  valuable  cross  between  the  dew- 
berry and  raspberry.    It  differs  from  both  its  ancestors  and  is  the 
first  absolutely  new  species  ever  produced  by  man. 

4.  A  cross  between  the  plum  and  apricot  called  the  "  Plumcot  " 
which  has  the  good  qualities  of  both  ancestors  and  some  of  its  own. 

5.  The  pitless  plum  and  thin-shelled  walnut  explain  themselves. 

6.  Among  flowers,  the  Shasta  daisy  six  inches  in  diameter,  and 
the  ten -inch  poppy,  are  well  known. 

He  works  by  cross-pollenation,  grafting,  and  rigid  selection. 
Specimens  are  collected  from  all  over  the  world,  raised  in  his 
gardens,  and  crossed  to  develop  desirable  characteristics.  They 
are  then  cultivated  in  enormous  numbers,  to  take  advantage  of  all 
possible  variations,  and  only  the  best  are  selected. 

Thus,  by  combining  a  deep  knowledge  of  biologic  laws,  with 


546  BIOLOGY  FOR  BEGINNERS 

marvelous  skill  in  their  use,  Mr.  Burbank  has  developed  plant 
breeding  to  a  degree  never  approached  before. 

COLLATERAL   READING 

Encyclopedia  references  on  all  persons  and  topics  mentioned.  Biology 
and  its  Makers,  Locy,  entire;  Main  Currents  of  Zoology,  Locy,  entire; 
Elementary  Biology,  Peabody  and  Hunt  (Malaria),  pp.  47-56,  Pt.  I; 
Life  of  Pasteur,  Frankland;  Children's  Stories  of  Great  Scientists,  Wright; 
General  Zoology,  Linville  and  Kelly,  pp.  436-451;  Zoology,  Parker  and 
Haswell,  pp.  628-649;  General  Principles  of  Zoology,  Hertwig,  pp.  7-67; 
General  Zoology,  Pearse,  pp.  6-12;  Manual  of  Zoology,  Hertwig-Kingsley, 
pp.  7-56;  Biology,  Calkins,  pp.  219-232  (Mendelism);  Mechanism  of 
Mendelian  Heredity,  Morgan,  etc.,  entire;  The  Next  Generation,  Jewett, 
pp.  20-24  (Mendelism). 


THE  HISTORICAL  DEVELOPMENT  OF  BIOLOGY     547 


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INDEX 


A 

abalone,  ornamental  use  of,  471. 

abdomen,  of  crayfish,  179;  of  grass- 
hopper, 197;  of  butterfly,  206;  of 
honey  bee,  213. 

absorption  (root),  53,  58;  selective, 
61;  in  an  animal,  375. 

acerata,  173;  use  as  insect  destroyers, 
472,  473;  mites  and  ticks,  473. 

acetic  acid,  461. 

Agramonte,  Dr.,  see  yellow  fever. 

agriculture,  close  association  with 
biology,  493. 

air  bladder,  of  fish,  245. 

alcohol,  plant  product,  461;  wood, 
462;  narcotic,  beverages  containing, 
514;  physical  effects  of  use  of,  SIS- 
SIS;  not  a  food,  516;  and  disease, 
519;  not  a  medicine,  520;  and 
efficiency,  521. 

alga?,  127. 

alimentary  canal,  363,  364. 

amoeba,  146-148. 

amphibia,  characteristics  of,  252;  use- 
ful as  insect  destroyers,  481. 

amylopsin,  374. 

animals,  general  uses  of,  467;  eco- 
nomic value  of,  468;  husbandry  of, 
489. 

antennae,  of  crayfish,  182;  of  grass- 
hopper, 194. 

anthers,  109,  113. 

anthrax,  137. 

anthropology,  333. 

antiseptics,  140. 

antitoxins,  138,  139. 

appendix,  322. 

apple,  structure  of,  120;  seed  dis- 
persal of,  121. 


arrowhead  from  the  Cave  of  Perigord, 

France,  334. 
arteries,  398. 
arthropods,      158;       characteristics, 

classes,  172;  classification,  173-177, 

235. 

ash,  121. 

assimilation,  5,  375,  377. 
astigmatism,  422. 
Atwater,  quoted  on  alcohol,  515. 
auditory  canal,  417. 
auricle,  397. 


B 

baboon,  318. 

bacteria,  4;  shapes,  133;  types,  134; 
methods  of  study  of,  135,  136; 
useful  forms  of,  136;  harmful,  137; 
defences  against,  137-141;  rapidity 
of  reproduction,  327;  useful,  447; 
nitrifying,  487;  good  and  bad  ac- 
tivities on  the  farm,  493. 

bacteriology,  134;  development  of, 
141. 

barley,  449. 

barnacles,  472. 

bass-wood,  seed,  122. 

bast,  root,  51,  56;  stem,  77;  fibers, 
78;  tubes,  78;  see  cotton,  flax, 
jute  and  hemp. 

bark,  structure  of,  76. 

baths,  431. 

beak,  of  bird,  289. 

bean,  structure  of,  34,  120. 

bee,  agent  in  pollenation,  110;  honey, 
structure  of ,  2 1 1-2 13 ;  queen,  drone, 
worker,  213. 

beetles,  beneficial  and  harmful,  476. 

Beri-beri,  356. 


549 


INDEX 


Biff  en,  Prof.  R.  H.,  his  experiments 
to  improve  wheat,  489. 

"Big  Trees"  (Sequoia)  of  California, 
81. 

bile,  functions  of,  373. 

biology,  definition  of,  1;  familiar,  2; 
value  of  study,  425;  application  to 
plant  improvement,  488;  to  plant 
protection,  489;  historical  develop- 
ment of,  535;  noted  names  in, 
547,  548. 

birds,  characteristics,  281;  structure, 
281-287;  habits  of,  294-306;  eco- 
nomic importance  of,  305,  481. 

bladder,  403. 

bladder-nut,  seed  of,  122. 

blood,  394;  changes  in  composition 
of,  396. 

brain,  408. 

branches,  opposite  and  alternate,  69; 
forked,  70. 

bronchi,  384. 

Brubacher,  Dr.,  quoted  on  alcohol, 
519. 

bubonic  plague,  151. 

buckwheat,  449. 

bud  (stem),  structure,  72. 

Burbank,  Luther,  noted  for  valuable 
services  in  plant  improvement,  489; 
examples  of  his  work,  545. 

butterfly,  structure,  205,  206;  meta- 
morphosis, 208-210. 


caffeine,  511. 

calorie,  344. 

calcium,  15,  17,  23. 

calyx,  109. 

cambium,    root,    51,    56;     stem,    78, 

80. 

capillaries,  398. 
carapace,  173,  179. 
carbohydrates,  20,  21,  23;    bulk  of 

man's  food,  344,  346. 
carbon,  14,  17;  circle,  527. 
carbon  dioxide,   13,    18,   23,   47;    in 

leaves,  91,  98,  382,  528. 


carnivora  (flesh  eaters),  313. 
Carrell,  Dr.,  treatment  for  infected 

wounds,  441,  541. 
Carrol,  Dr.,  see  yellow  fever, 
"castings,"  of  earthworm,  162,  165. 
catalpa,  121. 

cattle,  different  breeds  of,  491,  492. 
cells,    27,    30;     palisade    (leaf),    95; 

animal  (one-celled),  146-150,  158, 

198;    Hooke's  discovery  of,  537. 
cephalothorax     (head-thorax),     173, 

179. 

centipede,  173. 
cephalopods,    see    squid,    cuttlefish, 

octopus. 

cereal  grains,  447-450. 
Chittenden,  quoted  on  alcohol,  516. 
chocolate,  food  value  of,  511. 
cirrhosis  of  the  liver,  60  per  cent,  of 

deaths  caused  by  alcohol,  516. 
cerebellum,  409. 
cerebrum,  408. 
charcoal,  461. 
chemistry,  9. 
chimpanzee,  316. 
chlorophyll,  90,  92-93;    property  of, 

96,  129,  526. 
cholera,  137. 
choroid  coat,  419. 
chrysalis,  207. 
chyme,  371,  372. 
cilia,  of  paramoecium,  149. 
circulation,  of  earthworm,  162;    fish, 

244;    frog,   259;    bird,  287;    need 

for,    382;     development    of,    392; 

effect  of  alcohol  on,  516. 
civic  biology,  440. 
clams,  471. 

clematis,  seed  dispersal  of,  122,  124. 
cochlea,  418. 

cocoa,  452,  453;    food  value,  511. 
cocoon,  207. 
codfish,  value  of,  480. 
crelenterates,  469. 
coffee,  plant,  452;  effects  of  beverage, 

511. 

compounds,  9;   inorganic,  18,  19,  23. 
conjugation,  of  paramcecia,  150. 


INDEX 


cooking,  functions  of,  354. 

coral  polyp,  157;    coral  reefs,  470. 

cork,  harvesting,  460. 

corn,  structure  of,  36,  449. 

cornea,  421. 

corolla,  109,  110. 

corpuscles,  white,  138,  395;  red,  395. 

cortex,  root  cells,  51,  56;    stem,  78. 

cotton,  455;    Sea  Island,  458. 

cotyledons,  32,  44. 

crabs,  "soft  shell,"  188;   use  as  food, 

472. 

crayfish,  structure  of,  179-185. 
crop  rotation,  487,  488. 
Crustacea,  172,  179;    as  food,  472. 
culture  medium,  133,  135. 
cuttlefish,  produces  sepia,  472. 


D 

dandelion,  70,  121,  122. 

Darwin,  Charles,  his  "Origin  of 
Species  by  Natural  Selection," 
326;  chief  factors  to  account  for 
development  of  new  species  from 
common  ancestry,  327;  revolution- 
ized modern  thought,  541. 

Davenport,  331. 

deliquescent,  69 

diaphragm,  385,  387. 

dicotyledonous  (having  two  coty- 
ledons), 33,  79,  81. 

diet,  need  of  mixed,  346. 

digestive  system,  of  earthworm.  161; 
of  fish,  243;  of  frog,  258;  of  bird, 
287;  of  man,  363-375. 

diptera  (two- winged),  220. 

diphtheria,  137,  140. 

diseases,  eye,  137;  transmission  of 
by  insects,  232. 

"disease  germs,"  150;  prevention  of, 
442.  i 

disinfectants,  140. 

distillation  products,  from  plants 
(wood),  461. 

dogfish,  247. 

drainage,  regulated  by  forests,  447. 

drone,  213,  215. 


ducts,  root,  51,  56;    stem,  78. 

dyes,  vegetable,  461. 

drugs,  from  plants,  461;    danger  of 

drug  habit,  511. 
dysentery,  151;    caused  by  protozoa, 

469. 


ear,  various  locations  of,  416; 
structure  of  human,  417;  wax, 
418;  ache,  418;  infection  of,  432. 

earthworm,  157;  structure,  161,  162; 
locomotion,  162;  food,  value  of, 
165,  470. 

echinoderms,  470. 

Ehrlich,  Paul,  famous  for  method  of 
treating  syphilis,  540. 

elements  of  matter,  9. 

elm,  121. 

embryo,  plant,  31,  32,  43,  114;  de- 
velopment of  fish,  246;  study  of 
development  of  all  animals,  322 

embryological  resemblances,  322. 

endosperm,  31,  33,  113. 

energy,  342;    source  of,  526,  527. 

environment,  415. 

enzymes  (or  ferments),  363,  374. 

epidermis,  root,  50,  56;  stem,  78; 
leaf,  90. 

erosion,  497. 

erysipelas,  137. 

eustachian  tubes,  365,  417. 

evolution,  idea  and  evidences  of,  321, 
322;  method  of,  326;  of  life 
functions  of  plants,  532;  of  life 
functions  of  animals,  533. 

excretion,  6;  system  of  in  earth- 
worm, 162;  in  insecta,  198;  of  frog, 
261;  organs  of,  403;  effect  of 
alcohol  on,  517. 

excurrent,  69. 

exercise,  importance  of,  426-428; 
beneficial,  436. 

exo-skeleton,  of  crayfish,  180;  of 
grasshopper,  193. 

expiration  (breathing  out),  386,  387. 

eye,  structure  of  human,  419,  420; 
compared  to  camera,  421. 


552 


INDEX 


factory  and  housing  conditions,  443. 

fats,  20,  22,  23;  energy  producer, 
343,  346. 

feathers,  283. 

ferns,  127. 

fertilization,  plant,  108,  113,  114; 
of  fish  eggs,  247;  of  the  soil,  487. 

fever,  typhoid,  137,  142;  yellow, 
scarlet,  151,  469;  cattle  90. 

fiber  plants,  cotton,  455;  flax,  hemp, 
jute,  manila,  457;  coconut,  458. 

fibrinogen,  395. 

filament,  113. 

Fischer,  Professor  Irving,  quoted, 
434,  515. 

fishes,  structure,  239-246;  nest,  247; 
value  as  food,  480;  as  fertilizer, 
481. 

fission,  148. 

flax,  457,  459. 

Flexner,  Dr.,  American  scientist,  541. 

flint,  carved,  of  Old  Stone  Age,  338. 

flower,  function  and  structure  of,  108. 

fly,  house  (typhoid),  220;  danger 
from,  222,  223;  rate  of  repro- 
duction, 224. 

food,  definition,  342;  functions  of 
organic  and  inorganic,  343;  pro- 
portions, 345;  fuel,  starchy,  sugars, 
fats,  358;  building  and  repair 
(protein),  mineral  salts,  water, 
ballast  or  bulk,  359;  hard,  vita- 
mines,  360;  public  control  of,  441. 

forests,  value  of,  for  control  of  water 
supply,  495 ;  distribution  of  national 
forests,  496;  benefit  to  soil,  497; 
effect  on  climate,  497;  as  home  for 
birds  and  game,  498;  products  of, 
498;  enemies  of,  500,  501;  fires  in, 
501;  protection  of,  502;  reserves, 
rangers,  forestry  schools,  replanting, 
502. 

frog,  development  of,  253;  structure, 
254-261. 

fruit,  types  of,  118,  119;  functions 
of,  119;  structure,  120;  economic 


importance  of,  124-125;  use  as 
food,  455. 

fruit  tree  pests,  474. 

fuels,  use  of  plants  for,  458. 

fungi  (parasite),  127,  129;  examples, 
mushroom,  129;  rust,  smut,  mil- 
dew, mould,  130. 


G 

ganglia,  410. 

garden  pests,  potato  "bug,"  etc.,  475. 

gastric  fluid,  371. 

"General  Sherman"  tree   (Sequoia), 

81. 
geotropism,    the    response    of    plant 

parts  to  gravitation,  58;    positive, 

60,  62. 

germ,  diseases,  4;  sterilization  of,  141. 
germicides,  140. 
germination  (plant),  41. 
gills,   173;    of  arthropods,  182;    fish, 

241. 
glands,  368;    salivary,  369;    pyorlic, 

371;  intestinal,  liver,  373;  pancreas, 

374;  kidneys,  403. 
glycogen  (liver  starch),  374. 
gorilla,  316. 

Gorgas,  Col.  W.  C.,  229. 
grafting,  79. 

grasshopper,  193;  structure,  193-198. 
Grassi  and  Bignami,  231. 
grippe  and  colds,  137. 
ground-pines,  127. 
guano,  305. 
gullet,  of  man,  363,  370. 


H 

Harvey,  William,  circulation  of  the 
blood,  proved  by,  535;  portrait, 
536. 

habit  formation,  412,  413. 

haemoglobin,  388,  395. 

hawk-moth  posed  before  a  jimson- 
weed,  110. 

hearing,  sense  of,  416. 

heart,  action  of,  397. 


INDEX 


553 


heat,  11;  energy,  46. 

heliotropism,   the   response  of  plant 

parts  to  light,  88. 
hilum  (scar),  31,  34. 
homology,  184. 
hookworm,  166,  167. 
Hooke,    discovered    cell    walls,    537, 

538. 
horses,    breeding    and    selecting    for 

trotting,    running,    draught,    etc., 

493. 

horse-tails,  127. 
Hornaday,  Wm.  T.,  274,  -276. 
household  pests,  475. 
Hunter,  Arthur,  actuary,  N.  Y.  Life 

Ins.  Co.,  quoted  on  alcohol,  520. 
Hurty,  Dr.  J.  N.,  quoted  on  alcohol, 

521. 
Huxley,     Thomas     Henry,     English 

scientist,  211,  542. 
hydra,  157,  234. 

hydrogen,  12,  17,  19;   supply  of,  531. 
hydrotropism,  the  response  of  plant 

parts  to  water,  58,  61,  63. 
hygiene,  2,  4;    of  eye,  422,  425,  430; 

of  muscles,  426;    of  digestion,  428; 

of    respiration,    429;     of    bathing, 

431;    of  teeth,  432;    of  feet,  432; 

of  nerves,  433 ;  public,  437;  mental, 

437. 
hymenoptera     (membrane     winged), 

211. 

hypocotyl,   primitive   stem,    33;    ap- 
pears first,  42,  43. 


Iceland  moss,  457. 

immunity,  acquired,  139. 

indigo  shrub,  462. 

incubation,  300. 

influenza,  142. 

inorganic  matter,  1;    examples  of,  7, 

15,  19. 

inheritance,  328. 
insecta,  173;    classification,  193. 
insects,    agents    in    pollenation,    110, 

113;   and  disease,  220-232;   harm- 


ful and  useful  activities,  473,  474. 
inspiration  (breathing  in),  386,  387. 
intestines,  of  man,  363,  372,  373,  405. 
iron,  14,  17,  23. 
iron  oxide  (rust),  14. 
isinglass,  fish  product,  481. 


James,  William,  quoted,  413. 

jellyfish,  157. 

Jenner,  Dr.  Edward,  first  to  suggest 

vaccination  for  smallpox,  537. 
jute,  457;  see  bast. 


kernel  (seed),  31. 

kidneys,  403. 

King,  A.  F.  A.,  231. 

Koch,  Robert,  identified  bacteria  of 

tuberculosis    and    Asiatic    cholera, 

539. 


leaves,  functions  of,  86;  general 
structure,  87;  forms,  87;  arrange- 
ment, 88; .  heliotropism,  88;  modi- 
fications of,  88;  fall  of,  88;  other 
functions,  99;  use  for  food,  455. 

labium,  194,  212. 

labrum,  194,  212. 

Lamarck,  326. 

larva,  of  butterfly,  207;  forms  of, 
217. 

Lazear,  Dr.,  see  yellow  fever. 

legumes,  119;  importance  as  food, 
451,  452. 

lemurs,  318. 

lens,  of  eye,  of  camera,  420. 

lenticels,  75. 

lepidoptera  (scale  winged),  205;  harm- 
ful moths,  476. 

leprosy,  137. 

lichens,  127;  rock,  128;  Iceland  moss, 
455. 

lipoid,  355. 


554 


INDEX 


Lister,  Sir  Joseph,  developed  anti- 
septic surgery,  539. 

liver,  373,  405;    cirrhosis  of,  516. 

lobster,  185;    food  value,  472. 

lockjaw  (tetanus),  137,  140,  142. 

locomotion,  of  amceba  148;  of 
worm,  162;  of  crayfish,  186. 

locust,  193. 

Locy,  "Biology and  its  Makers,"  537. 

lumber,  production,  499;  careless 
lumbering,  500. 

lungs,  382-386,  404;  infection  of,  432. 

lymph,  382;    circulation  of,  400. 


M 

malaria,  151,  229;    see  protozoa. 

mammals,  characteristics  of,  310; 
valuable  for  food  and  clothing 
products,  482;  for  transportation 
and  as  pets,  483;  a  few  harmful, 
483. 

mammoth,  drawing  of,  from  Cave  of 
the  Madeleine,  France,  334. 

man,  314;  development  of,  321-325; 
primitive,  334;  Neanderthal,  335; 
implements  of  different  ages,  336; 
races  of,  340. 

mandibles,  of  crayfish,  182;  of  grass- 
hopper, 194;  of  honey  bee,  212. 

Manson  and  Ross,  231. 

mantis,  201. 

maple,  121;    "key,"  122. 

"Mark  Twain"  tree  (Sequoia),  83. 

marmosets,  318. 

mastication,  435. 

maxillae,  of  grasshopper,  194;  of 
honey  bee,  212. 

maxillipeds  (jaw  feet),  182. 

medulla,  spinal  bulb,  410. 

membrane,  mucous,  of  small  intestine 
of  dog,  372;  tympanic,  of  man.  417. 

Mendel,  Gregor,  his  "Law  of  In- 
heritance," 542-545. 

mental  hygiene,  433,  437. 

metamorphosis,  of  butterfly,  201,  208; 
of  amphibia,  252,  267. 

metazoans,  154;  forms  of,  157. 


Metchnikoff,  Russian  scientist,  his 
discovery  of  functions  of  white 
corpuscles,  540. 

microbes,  150. 

micropyle  (opening),  31,  35,  42,  113. 

migration,  of  birds,  300;  and  distri- 
bution of  Eskimo  curlew,  301. 

milk,  supervision  to  insure  pure,  441, 
442. 

milkweed,  121,  122,  123. 

mineral  compounds,  19. 

mineral  salts,  necessity  for,  353,  356, 
359. 

molluscs,  157,  234;  food  of  primitive 
man,  470. 

monkeys,  318. 

mosquito  224;  transmits  yellow 
fever,  225,  226;  eggs  of,  226; 
control  of,  227,  229;  transmits 
malaria,  231. 

mouth,  365. 

mussels,  471. 

monarch  butterfly,  metamorphosis  of, 
209,  210. 

monocotyledonous  (having  one  coty- 
ledon), 33,  79-81. 

mosses,  127. 

moth,  compared  with  butterfly,  210; 
harmful,  codlin,  tussock,  474. 

moulting,  of  crayfish,  187;  of  birds, 
284. 

mushrooms,  129,  455. 

myriopods,  173. 


N 

nasal  openings,  365. 

nectar  glands,  110. 

nervous  system,  of  earthworm,  162; 
of  arthropods,  172,  198,  199;  of 
fish,  244;  of  frog,  261;  of  bird, 
289;  of  man,  408;  effect  of  alcohol 
on,  517. 

nests,  of  orioles,  295;  of  humming 
bird,  296;  excavated,  woven,  296; 
built-up,  298. 

newt,  270. 

nitrogen,     12,     17;      fixation,     447; 


INDEX 


555 


supplied  to  the  soil,  487;    circle, 

529;  waste  of,  531. 
nodes,  68. 

nose,  adaptation  for  breathing,  384. 
nucleus  (amoeba),  147. 
nutrition,  5;    digestive  organs,  363; 

absorption,  375. 
nuts,  452. 

O 

oats,  449. 

octopus,  471. 

opsonins,  138. 

orang-utan,  318. 

organic  things,  1;   likeness  of,  6. 

organs,  27,  30;  "essential,"  112; 
specialized,  157;  homologous,  184, 
323;  rudimentary,  321;  digestive, 
363. 

oriole's  nest,  295. 

orthoptera  (straight  winged),  193. 

Osier,  Dr.,  quoted  on  alcohol,  519. 

osmosis,  definition,  58;  dependence 
of  root  absorption  on,  59;  suc- 
cessive, 61,  64,  65,  363;  absorption 
of  food  by,  374,  377;  and  life,  524- 
526. 

ovary,  109,  113;    in  frog,  263. 

oviduct,  in  frog,  263. 

ovules,  109,  113;  structure,  114. 

oxidation,  10;  of  tissue,  382;  and 
life,  526-531. 

oxygen,  10,  11,  17,  18,  19,  91,  98, 
103;  soluble  in  water,  186;  lymph 
supplied  with,  382;  plant  supply, 
447;  circle,  528;  properties  demon-- 
strated  by  Priestley,  1774,  537. 

oysters,  470;  "pearl,"  471. 


palate,  of  man,  365. 
pancreatic  fluid,  374. 
paper  materials,  from  plants,  459. 
papillae,  415. 

paramoecium,    148;     structure,    149; 

reproduction,  150;    parasitic,  150. 

parasites,   plant,    127,    129;     worms, 


164-167,  468. 
Pasteur,  Louis,  137,  141;    wonderful 

services   in   applied   biology,    538, 

539. 

pasteurization,  of  milk,  141. 
patent  medicines,  444. 
pea,  35;    seed  dispersal  of,  123. 
peat,  459. 
pellagra,  356. 
penetration  (soil),  42. 
pith,  stem,  79,  80. 
pepsin,  371. 
phosphates,  14. 
phosphorus,  14,  15,  17,  531. 
photosynthesis,    process    of    starch- 
making  in  leaves,  96-98;  compared 

with  respiration,  101,  103. 
physiology,  1. 
pigeons,  carrier,  306;  various  races  of, 

490. 

pine,  seed,  121,  122. 
pistil,  109. 
pitch,  461. 
plants,    general    uses    of,    446,    463; 

breeding  of,  488,  489. 
plasma,  394. 
pleurisy,  385. 
plumule,  32,  33. 
pollen,  109;    protection  of,  111,  113; 

structure,  114. 
pollenation,  108,  109;  cross,  109,113; 

biology  applied  to  methods  of,  488. 
polycotyledonous    (having    three    or 

more  cotyledons),  33;    stems,  81. 
pome,  119. 
poppy,  seed  of,  122. 
posture,  433. 

potassium,  15,  17,  23,  531. 
pneumonia,     137,     142;      effect     on 

alcohol  users,  519. 
ptomaine  (poisoning),  137. 
prawns,  as  food,  472. 
Priestley,  properties  of  oxygen  first 

demonstrated  by,  537. 
primates,  314. 
propolis,  216. 
proteids,  20,  21,  23;    function  of  in 

man's  food,  343,  344,  436. 


556 


INDEX 


protoplasm,    25,    27,    30,    41,    147; 

named  by  von  Mohl,   1841,  537; 

fundamental    material    of    plants 

and   animals    shown    by  Schultze, 

538. 
protozoa,    146;    parasitic,    150,    152, 

234,  327,  468;   as  scavengers,  469; 

diseases  caused  by,  469. 
pupa,  of  butterfly,  207. 
pure  food  and  drugs  law,  443,  444. 
pylorus,  372. 


rabies,  treatment  for,  538,  539;  see 
Pasteur. 

Redi,  discoveries  of,  535. 

Reed,  Dr.,  see  yellow  fever. 

reforestation,  502. 

rennin,  371. 

reproduction,  6;  function  of  the 
flower,  108;  by  spores,  127;  of 
bacteria,  134;  of  amoeba,  148; 
in  paramoecium,  150;  of  crayfish, 
187;  of  grasshopper,  200;  of 
honeybees,  214;  of  frog,  261,  267; 
of  birds,  298. 

reptiles,  273-278;  value  as  insect 
destroyers,  681. 

respiration,  5;  plant,  86,  93;  com- 
pared with  photosynthesis,  101; 
of  insects,  198;  of  frog,  260;  of 
bird,  287;  development  of,  382; 
hygiene,  429;  effect  of  alcohol  on, 
517. 

retina,  419. 

Rexford,  Frank  H.,  347. 

rheumatism,  432. 

rice,  449. 

rings,  annual,  see  wood  fibers. 

Rockefeller  Foundation,  442. 

rodents  (gnawers),  311;  destroy 
grain,  483. 

roots,  characteristics  of,  49;  structure 
of,  50;  function  of,  51;  normal, 
fibrous,  tap,  fleshy,  53,  54;  aerial, 
aquatic,  54;  adventitious:  brace, 
for  propagation,  54;  climbing, 


parasitic,  55;    hairs,  60;    pressure, 

61;  as  food,  454. 
rosin,  461. 
Roux,    bacteriologist,    142;     assisted 

in  developing  diphtheria  anti-toxin, 

539. 

rubber,  461. 

ruminants,  non-ruminants,    312. 
rye,  449. 


salamander,  271. 

salmon,  life  history  of,  248;  value  as 
food,  480. 

saliva,  370. 

salvia-flower,  111. 

sanitation,  4,  425. 

scales,  fish,  239. 

scallops,  470. 

scars,  leaf,  flower-bud,  fruit,  75; 
bud-scale,  76. 

Schleiden  and  Schwann,  proved  im- 
portance of  cell,  537. 

Schultze,  see  protoplasm. 

sclerotic  coat,  419. 

scorpion,  poisonous,  473. 

scurvy,  356. 

sea  anemone,  157. 

seed,  structure  of,  31;  growth  of,  34; 
function  of,  41;  development  of, 
113;  dispersal  of,  119,  122;  by 
wind,  water,  animal,  122-124. 

segments,  of  earthworm,  162;  of 
crayfish. 

semicircular  canals  (ear),  418. 

sensation,  6;  in  amoeba,  148;  organs 
of,  in  skin,  405;  "irritability"  of 
plants,  415. 

sepals,  109. 

serum  (blood),  395. 

sewage,  regulations  regarding,  442. 

shade  tree  pests,  474. 

sheep,  applied  biologic  methods  of 
breeding,  491. 

shrimps,  as  food,  472. 

sight,  sense  of,  419;    near,  far,  422. 

skin,  structure  and  functions,  404, 
405. 


INDEX 


557 


skull  cap  of  fossil  man-like  ape  of 
Java,  336. 

sleep,  434. 

sleeping  sickness,  151. 

slugs,  as  food,  471. 

smallpox,  139,  151;  see  protozoa, 
469. 

smell,  sense  of,  416. 

snails,  as  food,  471. 

snakes,  false  ideas  about,  274;  few 
dangerous,  274,  276;  poisonous, 
276;  treatment  for  bites,  276;  use- 
ful as  insect  destroyers,  481. 

sodium,  15,  17,  23. 

soil,  formation  of,  486;  composition, 
487;  maintaining  the,  487. 

solar  plexus,  411. 

Spencer,  Herbert,  quoted,  328;  ap- 
plied Darwin's  theories,  542. 

spermaries,  in  frog,  263. 

sperm  nucleus,  113. 

sphinx  moth,  207. 

spices,  454. 

spinal  bulb  (medulla),  410. 

spinal  cord,  410. 

spore-bearing  plants,  127;  classifi- 
cation of,  127;  as  food,  455. 

sponge,  155,  157,  234;  value  of,  468, 
469. 

squid,  use  as  fish  bait,  471. 

stamens,  109,  113. 

starch-making,  in  leaves,  91;  see 
photosynthesis. 

steapsin,  374. 

stems,  function  of,  68;  kinds  of: 
shortened,  70;  creeping,  climbing, 
71;  fleshy,  72;  use  as  food,  454. 

Stejneger,  Dr.,  276. 

stickleback,  247. 

stigma,  109. 

stomach,  of  man,  363,  370. 

stomates,  function  of,  91. 

stone  axe  head,  New  Stone  Age, 
338. 

style,  109,  113. 

sugar-cane,  456. 

sulphur,  13,  15,  17,  531. 

swimmerets,  182. 


sympathetic  system  of  nerve  ganglia 

411. 
syphilis,  137;  see  Ehrlich. 


tadpole,  267. 

tanning  materials,  from  plants,  461. 

tapeworm,  164-166. 

tar,  461. 

taste,  sense  of,  416. 

tea,  effects  of,  511. 

teeth,  decay,  137;   structure,  number 

and  kinds   of,   367,   368;    vertical 

section  of  tooth,  367;  care  of,  429; 

hygiene,  432. 

tegumen  (inner  seed  coat),  31,  38. 
test,  for  oxygen,  10,  18;   for  proteids, 

20;  for  starch,  22;  for  grape  sugar, 

22;  for  fats,  24. 
testa,  seed  coat,  31,  44. 
thistle,  121. 

thorax,  of  grasshopper,  196. 
timber,  uses  of,  460;    products,  498; 

structure,  503;   quarter  grain,  504. 
tissue,  27,  30. 
toad,  habits  of,  269. 
tobacco,  harmful  effects  of,  509-511. 
tongue,  of  man,  functions,  365-367. 
tonsils,  365;  infection  of,  432. 
touch,  sense  of,  415. 
tracheae,    173;    see   arthropods,    193; 

in  man,  365,  382,  384. 
trichina,  167. 
trachoma,  151. 
tree  toad  (hyla),  270. 
tuberculosis,  137;  effect  of  on  alcohol 

users,  519. 
turgescence,   the  expansion  of  plant 

cells  by  water,  58,  59. 
turpentine,  from  pine  pitch,  461. 
typhoid,  fever,  137,  142;  vaccination 

against,  441. 
trypsin,  374. 

U 

ungulates  (hoofed),  312. 
urine,  403. 


558 


INDEX 


vaccination,  139;  537. 

vacuole,  147. 

variation,  328. 

vascular  bundles,  80. 

veins,  399,  400. 

ventilation,  389,  429,  430. 

ventricle,  397. 

vertebrates,    158;     development    of, 

235;     classes    and    characteristics, 

236. 
Von  Behring,  a  German  bacteriologist, 

142;   helped  develop  anti-toxin  for 

diphtheria,  539. 
Von  Bunge,  Dr.,  quoted  on  alcohol 

515,  518. 
villi,  373. 
vitamines,  356. 

W 

Wallace,     Alfred     Russell,     English 

scientist,  328,  541. 
water,  19,  23;  necessity  of,  for  plants, 

58;     vapor,    91;     supervision    of 

supply,  441. 
wax,  215. 


wheat,  448,  449;   improved,  489. 
White,  Dr.  Andrew  D.,  quoted,  510. 
whooping  cough,  137. 
Wiley,  Dr.  Harvey,  521. 
Williams,    Dr.    H.    W.,    quoted,    on 

death  rate  in  World  War,  441. 
wind,  agent  in  pollenation,  111,  113. 
wood  (root),  51,  56;   stern,  76;   fiber, 

78;  hard  and  soft,  505. 
Woodhead,   Dr.,  quoted  on  alcohol, 

517. 

workers  (honey  bees),  213,  215. 
World  War,  low  loss  from  infectious 

diseases,  441. 
worms,  parasitic:  tape,  hook,  trichina, 

164-169,  234,  470;  see  earthworm. 


yellow  fever,  151;  conquest  of  by 
Drs.  Reed,  Carrol,  Lazear  and 
Agramonte,  229;  see  protozoa,  469. 

yeast  plants  (fungi),  130. 


zoology,  2. 


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